Counterpoint: XBox OS code base is now off of Windows 10 (ie: Windows 10 for XBox). A gaming OS, really, would just strip out some of the extra services that are running but most of them, outside all the extra crap that gets installed when you buy a PC from a vendor (adware, ‘helper’ apps) are somewhat required.
I am not sure I see that happening. Microsoft is moving more into a Cloud/Amazon/Google competitor mode but I don’t see Windows moving. I mean I really love my Linux Subsystem for Windows but when you are talking OS core, I don’t feel that Microsoft is going to abandon any of that.