I love these guessing games about the civs and/or sponsors in these civ games when a new addon is coming. I know there is a lot more to it then the sponsors (as there should be).
But first I had hoped for more sponsors since I found that only 8 was really a low amount for a game like this.
Even though I'm happy we get 4 more sponsors I had hoped for at least 6, but oh well, nothing to do about I guess (except using mods like I'm already do).
Since we already got the Arab sponsor that leaves only 3 to guess.
I think like everybody that some form of Japan (with or without Korea) is a safe bet.
Also a North-West European sponsor in some form is a good bet. My take on it would be something of Norway/Sweden and Germany and with them the descendent's of the flooded Netherlands, Flanders and Denmark This would be one of the 2 water themed sponsors I bet. This could also include the British Isles but maybe they keep them separate for a combo with Canada or something like that. (since I'm Dutch I really hope we at least get mentioned in this sponsor and not forgotton since our country ended up being at the bottom of the North Sea


)
The last one could be the for mentioned UK/CD combo or something completely new like a Caribbean alliance for the second water themed sponsor (if the JP/Korea combo isn't water themed). Or a Native Middle/South American themed sponsor.
Personaly I like the Caribean one the best for the final choice.
As Water themed sponsors they can make the North Europeans Water Engineers and The Caribbeans a sort of Pirate like faction. Japan/Korea I see more as a Science/Production Themed Sponsor. The Arabs they can make into a survivalists Themed Faction of sorts.
Probably I'm completely wrong but thats why it's called guessing.