Instead what'll most likely happen is the next releast of Windows desktop after 10 will be set up from the start as a service offering, and at the point where people sign up for it the ongoing charge aspects will be spelled out very clearly, including in the Ts and Cs. It'll be similar to how Office switched to the Online version - Superficially little change in the product, but clearly delineated with a separate deployment, branding, and versioning.
It can only be this way, because aside from the 'stealth' upgrades' that some 7/8 users encountered, a significant number of people bought windows 10 licensing, at retail. It would be a PR nightmare for Microsoft to attempt to invalidate ongoing OS usage rights for their Windows 10 user base, and they're not ignorant of that fact.