Along the lines of outposts (which I agree should return to the game as, at minimum, a functional alternative to forts), I would also like to propose the idea of a "town" or "village." Someone came up with the brilliant idea a few years back that settlers shouldn't actually found cities but towns, which would function as sort of proto-cities which would then evolve into cities after a set number of turns. The idea being that if you were ever forward settled by a civ, you could steal or raze their town before it became a city and avoid all the warmongering penalties. That wouldn't really be an "economic" mode, probably more of a "frontier" mode if anything. And, in the same line as towns, I think the goodyhut/barbarian camp system could use a bit of an overhaul by allowing you to keep them around as a tribal "village" district/improvement. I've never liked how simpler people were portrayed in civ as either goodyhuts or barbarians which in either case must be outright eliminated from the map, but maybe giving them a name and allowing you to incorporate them into your empire (maybe with particular tribal bonuses) would help humanize them a bit.