I am thinking one big war, but not one at a time. I think that when the appropriate number of years have passed, the new races should introduce themselves. Then we could see some kind of alliance negotiations (even Rebel/Empire), backstabbings, etc.. I think this should be one of the single-player AND multi-player game modes. Until the other players get to use their race, they could watch game messages (like say Sabotage, but not things like R&D, Jedi Training, etc.), observe battles, and even watch player's actions if those players say it's okay.