Might as well start it up, seeing as how it was just announced. Rumor is that it'll have night racing, weather, etc.
Coming Holiday 2011.
Realistically, we'll probably get Forza 3.5. Updated shaders for the cars, more cars, more tracks. Some sort of Kinetic experiences. Head tracking will be cool, if it's implemented throughout the game.
Note the steering wheel. Yep, T10 hard at work!