(01) Longer play time between eras, if you like the caveman play, you have an entire game to play discovering tools, how to fish, develop communication, only if you want to experience that era of play. As a option, or not an option for full length play.
(02) How about making the game, "The game," no numerical release dates, no Civ 1 2 3 4 5 6 7, but Civ. Always worked on, always updated, always expanded, with its own launcher, and standalone game as the game of all games CIV! Much like WoW or ESO. Updated mechanics, graphics, AI, Civs, Tweaks, Patches, It hasn't been done yet, I think Civ should be the game to do it.
(03) Obtaining geological maps from Apple, Google, and use actual 3D topographic geological flora from the maps to make realistic gameplay on actual maps. In scale also, feel like I'm in kindergarten playing with crayons that are 1-foot wide.
(04) Being rewarded for how I play, build, and my decisions I take, be in effect how I progress in tech, culture, or religion, or ability to build unknown but found wonders tucked into the game.
(05) Have the game have a cultural flow, as human nature really is, and not so much a calculator game. Passively see Einstein live and work and develop in your city, for a period of time, effecting science and Dinging physics a bit, or to say boost.
(06) Most players who are Civ players love to build, and like simulator games, I want to place a railroad from here to here, or decide to make the tunnel through that mountain, and depending on what edifices, how many civilians I route to work on that project how fast does it develop. Airports near major city's create better income, increased growth, civilian growth ect.
(07) Units in game have not numerical data on how well they perform, but as how they would perform in reality given by the actual historic data, no hp, no defense points, no attack points, similar to the TV show on History Channel where they put the fight between the two and see how they would win based upon weapons and ability's, but more detailed for the game, with heroics, and lore, both good and bad about the unit.
(08) Scenarios as a option throughout any gameplay, as optional, that would be like disasters, not only natural, but diplomacy changing events, like the hippy revolution. Not huge game changing events but could be small, and large like volcano eruptions.
(09) Varied styles of barbarians both friendly and hostile, with each of their own units, unique, rewarding, game changing, and formidable.
(10) Each turn shouldn't give a lot of stress on your machine, but rather allow you to have turn points each turn that allows multiple moves each turn, so its not so much, {Enter} click {Enter} early gameplay, and any interactive moves included in your turn moves towards an opponent or ally, the interactive other, not in his turn be able to respond during your move, the same amount of move points, or at half cost their own turns.
(11) Expansions that include American Indians, that have an entirely different city ethics, economy, units, ecological presence, and entirely different building, city's, tech trees. Also expansions such as the African Tribes, that are a large number of city states, with the AI and bonuses of a normal computer player, all fighting for tribal matters, about resources and land. Expand though conquer early and get the attention of several other tribes from the area around you.
(12) Different ways you can tech that can change the entire game, just like going with tesla electricity rather than Edison's. Being able to build Tesla towers across the expanse of your city and connecting to smaller others, not suffering from an upkeep of power lines, and soon through more expensive means have free power.
(13) Progression of wild technology's that change the entire tech tree of what is normal today as what "Is" our technology. Such as Germany winning WWI and WWII with all of their wild ideas, then change how the trains would develop. American Indians who dominate the world have the tech tree changed and Solar energy being developed in much different ways, say through a liquid of botanicals.
(14) Special people or Great people not be limited to a grandee of skill based upon historical figures, but a specialist in an area that was trained by your science district, with a train time of how much production you have in said science district to how much accumulative science you devoted entirely, would be able to passively boost any ground based production tiles in a relative 1 tile area around them until they have been used to uncover a underground "special" reserve or wonder, that you have indication, of its location, cannot build upon, but are eager to find out what.
(15) Tourism not limited to beachside resorts but also in later game be included to around wonders player made and/or found wonders and areas of national parks.
-Closed-