Not even the recent Civs scratch that itch for me. And Brian Reynolds seems to be in the mobile business now so....
As gameplay goes, newer Civs do have better AI (though it is still pretty dumb at times) but otherwise... They just feel lackluster somehow. (Strategic resources are OK addition though.)
Extensive terraforming, terrain height and depth, and moisture/wind are something that were ditched for no good reason. These things have happened and affect stuff on Earth, why not have them? (Eg Soviets fucked up Aral sea, i'd like to weaponize that effect in Civ games.)
Social engineering! Let me create my own style of government without getting limited to approximations of historical styles of ruling... With sufficient options, one could recreate historical styles, or create something new (and likely unworkable, but still).
And diplomacy! Feels like Alpha Centauri had the best UN-equivalent.
Hell, custom units would be fun to get back. What if my military strategy is built around an invention that later gets countered by others adopting similar style of warfare?
While i reckon good parts of ACs gameplay could be incorporated to games, topping its setting will be difficult. It is one of the finest works of science fiction ever created really.