I think they would be smarter to just add a analog like slider pad to their Surface tablets and Windows phones. And two discreet shoulder buttons.
IMO you really don't even need full controls on a tablet/phone to dramatically increase the gaming experience. It doesn't have to be a giant 360 controller layout.
The biggest problem is the lack of a direction input ... a small analog nub/dpad/stick solves that issue.
2 shoulder buttons would make most genres of games playable from sports games to FPS to racing games and platformers.







