The Microsoft business model is to sell Windows pre-installed on new computers. That's how they charge consumers for Windows.
I have a hard time seeing that regular consumers would pay a subscription fee for something that comes pre-installed and is necessary for operation. What if you buy a computer for someone else: Should you hand that person a payment plan?
No pre-installed OS comes with a subscription. Apple, Google and Microsoft all charge for software by tying it to hardware.
If Apple and Google can't do it, I don't think Microsoft can do it either. Think about this: Not even Apple can force their users to pay a subscription for software. Instead they make hardware "obsolete" by deteriorating software performance.
Windows is competing with Android/ChromeOS, MacOS/iOS and to a lesser extent Linux. Windows can not become "the OS that you have to pay for". It's bad marketing. Microsoft realizes this and bets on data-collection/ads instead.
For consumers I don't think Windows subscription will happen unless Apple and Google also move to subscription software.
There is a big difference between OS (necessary software) subscription and other optional software subscriptions (MS Office, Adobe Creative Cloud, Stardock Object Desktop etc.)