God I hope not.
It would be a waste of 2.5 bln dollars. The game division is just barely pulling profits for the first time, ever, so that's not smart. Also a good bit of why GTA IV makes so much bank is the install base of the consoles it's on. Had it been exclusive, it'd have *only* sold five or six million units versus ten or eleven as of now.
So that cuts the cost of the franchise in half.
Take 2 would make bank on the sale, but in the long run, it'd be a waste of money as every game would have it's profits cut due to only being out on one console. But Microsoft does need it's own dedicated sports games. I mean, Sony's MLB series is doing very well, and on a smaller userbase, has almost sold as much as 2Ks MLB 2K8 on a 2x bigger (american, where it matters) install base. It's pretty important for MS to tie down exclusivity where it matters, and having exclusive sports franchises that are good help any system.
GTA is a big name, but I feel that a lot of people feel let down after GTA IV. I'm not too certain that I myself will be a purchaser of GTA IV, but if it's anything like GTA IV, I'll pass. I hope if MS does this, they do weigh the options smart either way.