I have not read every post =yet=. But I will. first a few things off me chest.
I have a Mac. It is getting old, but still does pretty much what I need it to do (browse intarweb, watch anime), except play CIV 4 well. But for some design discussions, I think it is designed fine. It's just slow, bloated, and crashes; and has an annoying visual bug which can't be fixed (map graphics go all wonky). Today I had to wait about a whole hour for one turn to pass so I could make decisions for my civ (huge map 14 cities, renaisance era)...I decided to turn off the game.
I would like an
OnLive version
http://www.onlive.com/ this way one can play with maxed out graphics, huge map, lots of units etc without having to worry about graphics slowdowns, incompatible versions, etc
I would like Civs to start with one warrior and one scout, (Easy modes give one a worker as well.)AND the AI should attack your defenseless civ at the start if you are unlucky/dumb enough to leave your city undefended. WRT to that, we should not have to research hunting...we've been doing that for meeelyons of years already.
I would like
scouts to be more useful early on. Scouts can upgrade to be Spies, or (bring them back) Diplomats. They should have some stealth capabilities so they can watch without being snuffed out quickly, can attack wild animals (treat animals as their own civ instead of grouping with barbarians), Explorers can attack barbarians, Other scouts are better able to find scouts than normal units. The mechanic is similar to but incompatible with Fortify, call it Hide. Any unit can do this, scouts/explorers do it better. Units not moving or other actions, spend their movement points instead on Searching the squares they can move in, this is automatic. Most units have Heal/Fortify as their first automatic; Scouts and Explorers Heal/Hide first, Fortify must be chosen. Explorers can after fortifying fully, similarly Convert themselves to coastal Trading Posts, which extend Lines of Logistics to new lands or areas , after doing that they slowly convert to Colony which can do better, which is like a very friendly Goody Hut that won't turn against you, see below. Explorers can cross mountains.
Tribal Huts. I like some of the tribal drama stuff from Civ Rev, lets extend that to Civ 5. I also like the colonies from Civ3. This is an amalgam of those, and of the Hamlet-towns of civ 4. But first a pet peeve. I have a time wasting tendency to save/reload when confronted with the huts. This is stupid boring design.
First all ground and sea units can perform some diplomacy with other units, but scouts, spies, explorers, diplomats, caravels, etc, can do it better than most, and have contexts and different options which apply. All units can talk to visible units within movement radius, or are adjacent, e.g. Caravel next to a coastal hut. Also units can Raid nearby visible specific developed squares including Huts, within movement range instead of moving; this disrupts production on that square it does not destroy improvements, and nets some small variable cash for the attacker, this is automatic for units who not otherwise busy in hostile non-ZoC territory. Back to huts.
The huts are basically proto-civs, just use the non-main player/AI civs to stand in for them instead of barbarians. Or have a Hut civ as an alternative, or rework the barbarians so they can be neutral or friendly.
There are different Hut sizes similar to Hamlet-towns.
The tribal huts should not simply disappear when found. A unit which finds them is presented with choices about what to do, much like the special events in BtS. Instead of getting just one result automatically, one result (or multiple partial results) is rolled for success/partial success/failure.
A hut should have a unit on them defending them against barbarians and other enemies; animals do not move adjacent to huts. There is at least one Leader-warrior, and one scout. The scout wanders around the hut within a few squares radii. If the player or AI encounters this they can choose to fight it, which will provoke the huts defenses, and will be hostile some set of turns (just like angry citizens), if it has more than one warrior, it will leave the leader to defend, and send the other out to hunt down the offender, possibly attacking your civ.
They can of course be razed for money and if lucky and given Slavery civic a worker*, scouts cannot do this but do not provoke a barbaric response. An unsuccessful raze does not destroy the hut as hostile warrior(s) move out, your offending unit is pushed back to its' previous square it came from. A successful raze gets all the gold just like razing a hamlet-town. Failing to destroy an unhappy hut will allow it to generate hostile warriors for for every set of turns since the last fight with your forces...this can go on and on; so enraged, it will form a barbarian city if hostilities continue, and it must be destroyed or conquered. Hostile huts automatically gain full zone of control when hostile...they have been developing it all along.
In the event of success, the hut is friendly and depending on your choices and success roll, via continued trade adds to your civ some gold, and research per turn (just like a hamlet-town) rather than a lump sum or random tech, also to some extend they reveal a map of the surrounding area, not some random senseless quadrant, but an actual radius. In exchange for gold or whatever, a friendly hut can also perform some services, such as watch over an area to prevent animals barbarians from forming (adds to your visible squares), if it sits on a resource, this can be traded for, you can hire a spare warrior or scout (it is cheaper to use like to hire like). The closer to your civ the hut is, the friendlier it is likelier to be, If it gets within a cultural radius, it becomes a hamlet-town, depending on how friendly it is/was, and how long it has been left unmolested. A quest can also result from a good 1st response, which may net in turning the hut into a Settler (large Hut), or free worker (medium hut) or warrior (small hut). If holy relics/artifacts are in then this is another possible result of a Hut quest; only original huts can offer these.
A neutral response will result in nothing much happening, try again later. Or it may provoke a minor quest, =[ "go! Bring us the hides of 5 Bears, or we'll not trade with you." etc.
Some huts are formed from lost but surviving units who could not return home after losing contact with their civ.**; or they were surviving hamlet-towns from fallen cities outside a cultural border. Given a successful negotiation, these towns and units may be incorporated more successfully than unrelated Huts, especially if they were one's own units and towns. Attempts at incorporating a hut by a previously hostile civ can backfire, causing the hut to turn hostile or even barbarian.
If left unharmed long enough, and a main civ is destroyed, a big hut may form it's own civ, generally positive interactions with other civs may also encourage a big hut to form a civ if it is not too close. Negative interactions can cause it to join the barbarians.
*ZoC Zone of Control
my suggestion is that ZoC is available for units/armies not otherwise preoccupied. It is primarily limited by the movement range of the selected unit. It must be actively chosen in neutral territory, wherein one has the option to attack the moving unit or let it pass, possibly negotiating for money. Pushing ones way through is an option but provokes automatic attack. It must be developed over several turns, much like Fortify; it is automatic for defenders of cultural territory if they are not otherwise occupied, invaders must grow their ZoC against that. If your unit is healing, hiding, fortifying, moving, raiding, blockading, etc it cannot exercise a zone of control on adjacent squares. This is also like blockading, it prevents hostile trade/logistical lines, neutral ones must be negotiate piecemeal, Open Borders allows freely; blockading btw must also grow over the course of several turns. It can be done from either hiding or fortified positions once these are finished; however, fortified positions cancel hiding on that square. ZoCs only work on military units; ground and naval cannot influence each other except with bombardment or with units with the water crossing skill. That said, ZoCs cannot otherwise cross rivers either without Water Crossing skill. ZoCs grows better along Roads, adjacent rivers and coasts(not across them). ZoCs trip automatically against hostiles when a controlling unit is not hiding. Hiding units are given the choice to act, or allow passage of an enemy. Scouts and a few other units can ignore hostile ZoCs, possibly with skill checks. Occupying a constructed fort hastens a units growth of ZoC even in hostile borders.
**Logistical Lines
For most units, a continuous logistical line is needed to an owned, allied, or vassal civ. Continuous ZoCs in hostile territory, allow for logistical lines into enemy territory. Neutral territory does not need such, but a logistical line is needed, any hostile or non-open borders neutral cultural border blocks logistics. Ground units require clear logistical lines along the ground, ocean & coastal waters and mountains also block that for them. Explorers can hole up and form a Friendly Trading Post/colony to extend such lines given unblocked water logistical lines. Naval units require unblocked coasts, oceans initially block until later on. Units need to be in or adjacent to logistical lines to maintain control of the unit. In neutral territory, the unit is still visible but not under control, but it cannot normally heal and it will try to return to friendly logistics. In hostile territory, the player cannot get information from the unit, but it will try to return, and it cannot heal. Scouts, explorers, and any unit with Commando of course is excepted from the healing problem, units with Heal can only heal themselves. In either situation, if they cannot return, they may fight to the end, be captured by an enemy or surrender depending which unit initiates negotiation; in neutral territory, they will hole up as close as they can to friendly border and wait, if they wait too long, they give up and form a Hut or go barbarian, they can also be bought by another civ. Which brings up mercenaries.
Mercenaries
Currently one can ask another civ to join in a fight. For Civ 5, a civ can request a specific action by a specific unit, lease or purchase trade units from that civ. Writting Tech needed.
Writing is not need for units to bribe other distinct units not to attack, allow passage, rebel, give intelligence, or join the opposition. Scouts, explorers, and especially diplomats and units with Leadership are better at that stuff as well as countering such (spies counter). Like or unlike properties between units also affect success e.g. religion.
Other stuff.
Natural channels. Isthmus are already in Civ4 when connecting two diagonally adjacent land squares otherwise surrounded by water, these block ships and shipping. But there should also be natural channels as alternative, allowing ships and sea logistics to pass. Land traffic is not fundamentally halted. Cannot build roads or rails until advanced steels become available.
Islands groups. Basically squares usable by both land and sea units, both limit movement to 1, and both receive 25% defensive terrain bonus. Land units with Water Crossing don't have movement limited. Cities cannot be formed on them, but hamlets can be. Can be defined also as a freshwater lake with islands which allows ships, and land units. no roads or rails.
Wetlands, lakelands, marshes. Basically, oasis for non-desert squares. Limits movement, provides water if freshwater, not saltwater marshes. but does not allow ships, does allow roads and rails. Cities can be built on them, but inlike oasis adds

.
I don't like workers much. most of their functions can be replaced with work orders within the Fat Cross via the city screen by assigning population, or spending money. Any specific work within cultural borders but possibly not in the Fat Cross should require just some cash, ie connecting cities with roads, just like in CivRev.
Engineering allows for construction of
passes & tunnels in otherwise impassable mountains, once built, Forts and mines may be built there. These roads may be deliberately inaccessible from one side, the side not started adjacent to an existing owned road. I hate the lack of utility of Mountains in Civ4. Volcanoes may not be built on at all.
Military engineer. A unit which can damage defenses, but does not bombard, can also make fortifications useful against gunpowder units.
Resource depletion. Alternative to treechopping and applicable to other resources. Assign a population in a fat cross, to a spot, normally it can draw resources indefinitely, tell it to over produce and it will produce greater resources for a while. This will eventually alter the terrain: the trees disappear, grass land turns to prairie, prairie turns to desert. Special resources such as fish go away permanently after too much depletion. Left alone some of these replete if there are still some left. Mines do not replete, but they can also turn to desert with overmining, they will eventually deplete entirely even without overmining; similarly with Oil. Like Mathematics tech improved woodchopping yields, techs can ameliorate depletion or just generally improve yields without risking depletion. Some special resources can popup elsewhere, game, fish, whales etc can emerge in areas left untouched. These start small and must grow to achieve the potential.
The larger your resources, the less effect owning a special resource has, too many specials has diminishing effect too. Trade for what you need.
Tech Research
More like the Spy control by adding Weights of

to respective technologies.
That's all for now. Maybe more later.