Highly doubt it. There aren't enough 360 exclusives.
That said, I'm super hyped for this game. Even if it does end up just being a SSBB ripoff, I'll be fine, considering I never played much Nintendo growing up. Playstaion kids, unite!
Let's see.
We could have Master Chief, Noble 6, The guy from Halo ODST, Marcus Fenix and Co from Gears of War, Alan Wake, Issac from Dead Space, Splosion Man, Frank West.
And it doesn't have to be Xbox exclusive. SSBB Has Sonic and Solid Snake.
We could have really anyone from an Xbox game even if they are on other consoles.
So that means. Altair, Desmond, Ezio and Connor from Assassin's Creed, Alex Mercer and James Heller from Prototype, Sam Fisher from Splinter Cell, The Prince Of Persia, John Marston from Red Dead Redemption, Ryu Hiabusa from Ninja Gaiden, And of course Garret from the Thief games. That's just of the top of my head. So if Microsoft did go this route we would have a good roster of fighter's.