The question remains, what civilizations would make it if there was an AoM II?
The first AoM focused on Europe, and then had a really crappy X-pack with a fake civilization. Perhaps if ES's second AoM is made with more variety? Added that, there might as well be a 2nd X-pack for this AoM II!!! 
Here's my idea...
AoM II: War of the Gods (Which would be the original game)
5 European Cultures and 1 African Cultures
- Greek (Southeastern Europe) or Greco-Roman (Southern and Southeastern Europe).
- Norse (Northern Europe and Scandinavia).
- Celtic (British Isles and Western Europe)
- Roman (Southern Europe, if Greco-Roman is not made).
- Slavic (Eastern Europe).
- Egyptian (North Africa).
The 3 civilizations (Greek, Norse, and Egyptian) would be "improved" versions of the original civilizations from AoM.
The Romans would have to get some similarities with the Greek Gods, but their Gods should have different advantages. Of course, everybody knows the Romans took several ideas from the Greeks, but the Romans made out of the Greek idea their own unique thing.
Then again, ES could just call a mix-civ "Greco-Roman" and keep the Greek and Roman fans happy. Also, they could find a spot for Egypt, but I have a better option for it.
Since the Egyptians, Greeks, and Norse civilizations would basically be improvements of the original, there would actually be 3 new civilizations: Celtic, Roman, and Slavic.
The first game would basically focus on Europe.
AoM II: American Mythology
3 or 4 Mythologies from America
- Aztec (Central America).
- Inca (South America).
- Lakota (North America--Central).
- Navajo or Cherokee (Maybe).
Aztec and Maya mythologies would be too much alike, and the Aztec mythology is much more complex and by far more known than the Mayan mythology. The Lakota also had a very complex mythology, and they could go very well as the representatives from the center of the U.S.
The Inca mythology was by far the most complex in the South American region, specially since they (like the Romans) took in the mythologies of various of the cultures they conquered. I'd get really pissed-off if ES doesn't include them in an "American" AoM X-pack.
As for the Navajo or Cherokee, I don't think ES would make more than 4 civilizations. It would be neat if they would let go of the dumb idea of secluding themselves to just 3 civs. per X-pack, added that a 4th civ. would be a nice add-on to the variety of N.American Mythology.
AoM II: Global Mythology
5 or 4 cultures
- Chinese.
- Japanese.
- Hindu.
- Arabian.
- Zulu.
I like Arabian mythology, mainly because of the genies, the flying carpets, and all those other neat things.
*Imagines using genies to blast enemies*
Hindu Mythology is perhaps a "maybe" since there are current practicioners of the religion, and they might find it insulting that their people are killing each other in a game (You know how the religious folk are about these things). 
Minor Tribes?
I don't think AoM II would need Minor Tribes like in AoE. They would have little to no purpose in the game with civilizations that have mythological monsters as units. 
Maps
By using logic, the European maps would focus on peninsulas, the mediterranean, the British isles, and Scandinavia/Northern Europe (cold).
The American maps would have the Tropical Jungles (Aztecs), the Andean Mountains (Inca), the Plains (Lakota), and some other parts (Maybe the Amazon).
As for Asia, they'll probably have maps more or less like the ones right now for TAD. 
Campaigns
Probably some guy traveling around the world? Not sure, it would have to be something mythologically related. Maybe it could be about a person in the future or modern times that goes back in time to the "Age of Mythology" and travels from culture to culture. 
Either that, or historical-mythological campaigns.
Hope you like the ideas. 