In all honesty i think it will be either (East) Asia (korea/siam/etc.) or Baltic (Denmark and Poland).
I don’t think it will be middle-eastern though an Asian pack might include Persia.
They are not going to add more maps so i think it is a safe bet that any civ from outside of the current map pool/groupings is unlikely, esp. something like Polynesia where half the value would be the maps.
I hope we wont see something like Spain 3.0. we have enough Spanish civs in the game.