Personally id prefer it if you do "normal" games between the various alterations your coming up with, just to make sure it doesn;t warp into some sort of madscientesque alternative reality series. Having alterations isn;t bad, just keep them seperated from eachover by normal games.
You have promised games as Greece and America if I recall correctly. And id be interested to see an ancient era civ game as Babylon (preferably including arabs considering they did exist before the coming of Islam and without sumer)
---
An always was game as a European civ in a "medieval era civilisations only" game would be interesting. Although after a normal game first.