if i might add this at this point in the discussion:
i think civ needs a mechanic for simulating nomad style civilizations like the skythes, mongols, huns and others around. they wouldnt depend on city building but could live roaming around.
i know its hard to imagine something workable but i already thought about when i was thinking of an acient persia/greece map.
darius the second i suppose tried to conquer the skythes but they just lifted their settlements and ran away into the vast territory of the north while darius' army was slowing going out of provisions. he just couldnt conquer that kind of mobile civilization.
there should be something to give a civilization that flavor, along with a way of keeping territory unoccupied for a longer period of time (larger maps with fewer civs?)...
My short (and quite old, in the meantime) concept to achieve this: temporary encampments.
The problem with all these ideas: The would need totally new algorithms to work, a totally new AI! New code, that would need new testing, patching, balance evaluation and so on and so forth.
As nice and interesting as it would be to have such unique playstyles - it will never happen. Exacly because of this: The code will be too unique and only be used for one civ. And therefore not worth the effort. (For a money orientated enterprise, at least. And I can not blame them for this, by the way!)