Microsoft is probably going to make a lot of money from selling apps/games on win-10. Why would they lose that for and commoditize their OS and the API layer ?
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".