Here are some of my thoughts on balancing going into BNW and beyond to patches/ future expansions. Some of it is addendum to what was already discussed in the thread so far.
Era Science Balance: I am one of those people who favors a little more hang time to enjoy the tactics of each era. I still like for the balance between victory conditions obviously, I just favor a more fleshed out standard speed experience. My suggestion is for the progression into new eras to be slightly slower by halting vertical progress through this system: Offering the advantage that the tech leader may enter the next era by researching the first tech whereas the other civs (who have all met eachother) must tech "flat" to achieve the next era. Each subsequent era can allow for more leaders or more techs to be plucked from the following era. The tech leader or leaders in later eras are able to enjoy their lead by back-tracking to balance out their tech paths and prepare to achieve the lead again next era. They may potentially, if on a roll, be allowed to go in 2 techs deep or even 3 or more in the late game if they are first to the next era again and again. You would not be allowed to be two eras ahead of civs who are getting the "known civ" bonus from your discoveries, so, for example - your continent could still be way ahead in tech versus the other undiscovered continent but it will eventually balance out. This pause for science also allows the weak links of the game to get caught up or killed off naturally to get the game rolling again. Great scientists bulbing could be "buffed" to allow you to grab techs that are locked to you in the next era but that you would otherwise be able to research via the normal tech path, though you could still not get into into the industrial if everyone else was is in medieval.
If the tech leader was a civ like France they could grab early musketeers or a tech leader Korea might be able to get H'watchas while everyone else is still in the classical. Scientists might need to start showing up a little faster to make this re-balancing more interesting. Don't know where to start for keeping it balanced in the current math of the game but I believe it is very doable by the devs and will not make the game a slave to realism. And I hold no attachment to the "exactitude" of my idea so it could easily be tweaked around.
AI Surrender Balance I mentioned some of my thoughts about the AI offering the player unacceptable peace treaties in the "nitpick" thread, but I wanted to share about AI vs AI surrenders. These can introduce game-breaking imbalance at higher difficulties. When the AI accepts another AI's godawful peace conditions it can be far too absurd for the victor who can easily handle 2-4 high pop puppets no problem and thus instantly start down the path to being a runaway.
Anecdote re: Surrender Balance...
Unit Upgrade Paths + New Unit and Promotion Ideas:
First thing: remove insta-heal. Second thing: Units that change in nature from ranged to melee or from melee to ranged get to re-pick all promotions upon upgrade.
Scouting Line, (exploration tree idea, first 4 scout units cost no maintenance/ or maybe they cost nothing to upgrade..):
Scout Unit Line
Scout
NEW: Medieval Scout?
NEW: Dragoon/Light Dragoon? (Ranged attack 1)
NEW: Halftrack? (Ranged attack 1)
Mechanized Infantry (Ranged attack 1)
Spearmen Unit Line, (Cannot get cover promotions, instead get engagement promotion line which commits enemies through zone of control)
Engagement I: Enemies cannot melee attack against this unit and then move away. Fortification bonus increased by 10%
Engagement II: Enemies who move adjacent to this unit lose all but 1 movement point unless they enter the tile with 0 moves left. (They are engaged and must either fight or end turn) Fortification bonus increased to 20% total
Note: This idea makes for a very interesting twist when the Lightening Warfare Autocracy tenet gets adopted. Really nice imho.
Spearmen
Pikemen
Lancer (If it cannot fortify, at least give it this: Gets/gives neighboring units an additional flanking bonus. Goes away on upgrade)
Anti-Tank Gun (Ranged attack 1 or 2)
Helicopter (Ranged attack 2, can fly over coastal tiles without embarking but loses hp per turn)
Melee Line:
Swordsman and above starts with Cover 1 or perhaps Siege?
Siege Line:
Promotion that setting up costs 0 moves (perhaps this instead of cover?)
City Defense Changes:
Ranged attacks used against a city (by archers for example) are first absorbed by and kill the GARRISONED UNIT. The garrisoned unit heals approximately 5 or 10hp(?) each turn when it moves/attacks but it counts as fortified either way if there are walls present (50% fortification bonus to unit?). Any unit may receive the fortification bonus regardless of unit line. Tradition improves these bonuses. Units that perform no action while stationed in a city heal as normal.
Siege and melee attacks against a city damage the CITY, ignoring the garrisoned unit.
Guided Missile Change:
Guided missiles do a large amount of bonus damage to garrisoned and fortified units. Automatically kills civilian units who are not covered by a military unit. Firing a guided missile at an unoccupied tile pillages ALL improvements (no gold received). - The reason for this harkens to the game I mentioned earlier. Had I been able to fire a guided missile at the enemy railroad network between the two cities I was spying on (one of which was building the last spaceship part), I could have really improved my chances of victory due to tactical superiority. I hope the AI could be programmed to do the same.
Thanks for reading my suggestions!
More than four that is.
and they're actually decent tiles especially in the early game. It does apply to floodplains, yes, but I honestly have a lot of trouble finding these long stretches of usable Floodplains that aren't just entirely flat with 0 production and surrounded by worthless Desert. I see it as a way to compensate for what should be bad start, but Petra then turns into a god-tier start, hence why I see Petra as the problem child. 
1
and with incense you're lucky if it's not a desert tile which means zero food, zero hammers. 
