I think i am the first to start this topic.
We have had Shogun (japan), Mongolian Invasion, Medieval, Viking Invasion, Rome.
My next guess would be that it would be set in China circa 600-200BC. Spring/Autumn, 7 kingdoms time periods. (It seems like a rather grand scope though.
Also, how about from New World 1492-1776 (but i feel that this scope is no exactly "Total War"), which is the same time period as Sid Meier's Colonization. (More concentration on gunpowder units, and application on how to balance the native american's and European Powers)