I wasn't really surprised to see this news [vg247] about Microsoft registering some Microsoft/Sony related domains. In all likelihood, it is something to do with either Windows-powered Sony tablets (like future versions of the S1 and S2 running Windows 8) or Vaio PCs running Windows 7/8.
But, one tiny part of my soul wonders that, since Microsoft doesn't have a portable gaming device and isn't releasing a portable gaming device (phones/tablets not really counting, as they're all third-party products) that it might just be thinking about letting SOME of its third-party core gaming titles roll over to the Sony Vita or adopt an own-branded version (Microsoft Xbox-Go or something).
Now, don't expect to see Halo running on a Sony platform, but why not throw out a version of Forza to compete with, what will presumably be a much delayed, Gran Turismo on the Vita. Not only will it eat into GT's sales and sell millions in its own right, but could nudge Japanese gamers (which MS still lusts after) into getting an Xbox to play the next big-screen version.
Similarly, Viva Pinata, Perfect Dark and some other older series could well get a revitalising kick if shared around on another platform. Never mind some of MS's old PC franchises like MechWarrior, Train Simulator (which would go down a storm in Japan on a handheld) and so on.
Sure, this is probably just wishful thinking and there are any number of good reasons why it won't happen, but hey - lunatics only have to be right once every now and again.