Nope, what sunk Longhorn was politics.

Windows team is a C++ kingdom, and those devs will not adopt .NET even at gun point.

They redid Longhorn with COM and called it WinRT, irony of ironies, WinRT applications run slower than .NET with COM reference counting all over the place.

Google has showed those folks what happens when everyone plays on the same team, and now it owns the mobile phone market, a managed userspace with 70% world market.