The posts so far seem to be a wish list. I'd venture that as per the name and basis, the civs will be chosen based on 3 distinct scenarios, as that's all it sounds like the expansion will be. As such, with Sumerians and Hittites already on the list to go with Babylon and/or Persia, I'd guess something else that fits the time lines and goegraphic areas. It would likely also have to be civs that were true empires or significant powers. So the Inuit are not a likely choice, although ancient Israel could be a possibility.
My guesses for scenarios and possibilities for civs would be:
Cradle of Civilization: ancient Israel, Phillistines, Caananites, Phoenecians, Ethiopia / Axum,
Meso-America: Olmec, Toltec, Anasazi,
Africa: Mali / Songhai, Asante / Dahomey, Shona, Kush / Nubia, Ethiopia / Axum
Far East: Angkor / Khmer