Microsoft's silence on the issue speaks volumes. The fact they are not directly answering it suggests Windows 10 or its following versions will be subscription.

My guess is that if you're not one of the people who upgrades in the next year. You will be paying for it annually. Again, this is total speculation.

I hope that Microsoft can reach some middle ground like they did with Office 365 and still offer a perpetual license version. E.g. Office 365 and Office 2013. Windows 365 and Windows 10. My guess is that they will play it by ear.

Let's keep it real, offering "Windows-as-a-service" is really about the money. The end-user gains little benefit. I'm always hesitant about moving critical system infrastructure to the cloud. Even AC in the Cloud doesn't make much sense to me since it's updated so infrequently and it's not like it requires constant maintenance.