The obvious problem with limiting AAA games to a single platform is there'll be a massive revenue drop from reduced sales. While it might force a few ardent gamers to buy an XBox, many are likely to just be pissed off by the move and not buy the game.
So it seems like MS limiting any release to XBox and some PCs would be shooting themselves in the foot.
Which probably means that's exactly what they'll try. Perhaps not immediately after the sale goes through (if it goes through). Give it a year, two years max before they start trying to make everything a "platform exclusive".