If we dismiss civs that are kinda-sorta-already in game like Parthia or Medes (Persia), Macedonia (Greece), Phoenicians (Carthage), Byzantine Empire (Rome) and all the tribes, whats left from approximately same region/period?
* Sumeria
* Kingdom of Israel
* India - further away but close enough for Alexander to reach

* Kingdom of Armenia maybe?
And of course it can always be a different region. Khmer, China, Vietnam. Or even America - Olmecs, Zapotecs.
My bet is on India unless it's gonna be the new-region themed expansion, i.e. Eastern Asia.