My guess: It'll be a lot like how Android works. The kernel is OSS, but "Windows(Google) Services" requires a proprietary license.

Android's license is "you need to put the Google Play Store and the Google App ecosystem on the phone". Window's license might still be, "pay us money".

You wouldn't pay for the kernel (because of GPL) but you would pay for branding and support (like RHEL) and you would pay for the ability to run the "Windows Application Compatibility Layer".