Well at the end of Revelations he says he knows where the other apple is so maybe you are another assassin but in the end get the apple and transistion to the Desmond one.
The next is confirmed to at least partially take place in Egypt, though I have no idea when or as whom.
As far as i know AC3 is going to be the last one. And i myself would actually want it to play out somewere else than Europe or the Middel East. It would be very interesting if the series ended in Africa. OR it would be gloriously awesome if you could explore totally diffrent citys/towns on diffrent continents. I would Scream like a little girl if i could explore Timbuktoe,London and Mumbai in one single AC game.
Ubisoft already hinted that it is going to take place in Egypt, for sure. I assume, from what I have read in the AC:Wikia; that it's going to be taken place as one of Altiar's family members. (Who had several of the memory holders, as mentioned near Altair's death scene before he goes into the Vault).
while the American Revolution would be pretty badass I doubt they'll go there. Ubisoft as a company is French and the French revolution hasn't been as explored within the realms of movies or games so I think your suggestion of the French Revolution would be more likely and equally as awesome!
After playing and beating revelations I believe that the next game should be Desmond solely but ubisoft already hinted egypt so I think we wont get that until later on. Altair would be good too see more of in his own time period. Ezio however has done all he is required to do. Therefore I think either Desmond or a new assassin entirely would be the way to go. The possibilities are endless at this point, I am confident Ubisoft can keep the ball rolling for they have never let me down.