I think that we will have not "the most important" civs, only the civs which are needed by scenarios included in this add-on. I'm also quite pessimistic if there will be Poland, but as our Golden Age occurred exactly in the period 'Beyond the Sword' so, maybe we will be finally in.
My list of civ:
Portugal
Dutch
Native North-Americans (I think it will be one general civ like Vikings)
Babylon (great choice!)
Poland
Austria or Austria-Hungary (rather Austria
)
Some south-Asian like Khmer, Siam
Some African like Ethiopia
One one native American, I'm afraid, from Central or South America
one is still missing - maybe Hittites?
My list of civ:
Portugal
Dutch
Native North-Americans (I think it will be one general civ like Vikings)
Babylon (great choice!)
Poland
Austria or Austria-Hungary (rather Austria

Some south-Asian like Khmer, Siam
Some African like Ethiopia
One one native American, I'm afraid, from Central or South America
one is still missing - maybe Hittites?