Well,from the 8 already revealed Civs,only 2 of them have their first time as a playable civilization(Austria and Huns) . For that reason,I suspect the 9th civ won't be Zulu or any other that was playable in other Civilizations .
Thats makes sense. It has to be a surprise. I think it depends on the Into the Renaissance scenario, and when it begins. The last civ must be based on that since it is the central theme of the entire expansion.