Ben Thompson at Stratchery proposes just that. Two companies - one that's Windows, Windows Phone, Surface and Xbox and the second would include business like Office, Azure, Bing, Skype and OneDrive. I think this makes sense but also don't see it ever happening because Microsoft's culture is so deeply tied to Windows.
http://stratechery.com/2014/making-sense-microsoft/
http://stratechery.com/2014/making-sense-microsoft/