They can't stay married to Wintel without some diversity and Microsoft is being a bunch of dicks with their ARM efforts in terms of creating an Apple-like platform. Hence all of their efforts with Macs, Linux and now their own hardware efforts. It's a smart move, they just need to be careful to partner up instead of trying to manufacture themselves which I'm sure is what they will do.
Ideally they would have some sort of Steam set top box that you could buy and throw onto your TV. The difficult part is accommodating the input controls. Gamepad is fine and all but many games are better with the KB/M and I don't doubt a significant portion of their potential customers would want to play them that way.