Either feudal Japan or medieval China, preferably the later for its sweeping set pieces. I'm very wary of setting an AC game in an era with guns. So that knocks out all the other options but Egypt and Ancient Rome. We've already done Rome, twice, so thats out. Ancient egypt would be allright, but i think an Oreintal culture would provide some nice variety. AC1: arabian, AC2: Western, AC3: Eastern. Would really flush out the sense of the templars being this vast shadowy hegemony.