This move is a hedge against Apple and is not about gaming as much as it is about maintaining Windows client side hegemony.

Apple is almost certainly planning to release AR/VR headset in the near future, this raises the question; what hardware is going to be used to power this headset; I'd bet Apple is working on a console like iDevice, or probably more likely an external GPU, that can be used with any Apple device.

Now imagine if Apple decides, admittingly in a very un-Apple like fashion, to allow anyone to run MacOS on their iPads, and iPhones; what that would do to consumer Windows market share.

This primarily establishes a moat against Apple, not Sony, and protects consumer Windows, not Xbox.