Interesting thread with lots of very interesting replies. Good job, guys.
Nintendo:
The Resistance series from Sony goes to Retro. It has nifty weapons and a dark atmosphere. Would be interesting. It might be a lower tier shooter on Playstation but on a Nintendo system it would be unique.
Microsoft:
The Kirby series from Nintendo goes to Rare. That means Kinect, probably, but it might turn out fun.
Sony:
The Fable series from Microsoft goes to Naughty Dog. I think they could turn it into something special.