In the Left 4 Dead 2-expansion The Passing, which was just released, Valve teases Dead Rising again. On a wall the following text can be found:
Out of film, No Helicopter
Zombies are too fast.
Not going to make it,
This is not the first time Left 4 Dead and Dead Rising go up against each other, and with Dead Rising 2 on the way we don't expect it to be the last either...