So what's your take on Win 10 going to a subscription service? Like would you go to it when Win 7 is unsupported and becomes unviable/unsafe as a net connected machine?
This wasn't directed at me, but I don't think you have to worry about that. MS operates similar to Google now. They target all users inclusive poor users in India and other places with even lower income.
Google lets handset makers make official Google backed Android phones if they include Google Play services. The agreement is that all handsets from the handset maker must include Google Play services. That's why no Android handset maker dares to make an Android phone without Google Play services. Because then they would never be allowed to make a phone which uses Google Play services. Google wants data and users so it doesn't drive costs higher than even the poorest can afford. Google has even released special low-bandwidth Android phones for those who have a hard time paying for data consumption.
Microsoft is very similar to Google. It wants Windows 10 everywhere. I don't think devices with screen size under 10" even require a license fee. Windows 10 for Raspberry Pi is free.
So I would be willing to bet the farm (luckily I have no farm), that we won't see Windows subscription in the consumer space.
What can happen in the next decade is that Windows 10 may come with "S mode" by default on new computers. Today it's free to unlock "S mode" computers, but I think MS will start charging $50+ for unlocking "real Windows" once the Windows 7 userbase is small enough. But that will only apply to new computers. You can freely use Windows 10 on existing hardware until Windows 10 doesn't support your hardware anymore.
Subscription would be counter productive for Microsoft. They have a Store with software they want to sell, but right now half the userbase is on Windows 7 and another 100 million or so are using Windows 8.1 and even XP.
If a lower cost option like Linux would become a threat (like it was on netbooks ten years ago), Microsoft simply gives Windows away for free. It's about market dominance, not about extracting the last dollar from poor people.
If you can afford roof over your head, water and bread, you'll be able to afford Windows too. What Microsoft has done with Windows 10 is the opposite of what Apple has done with macOS which is clearly aimed at rich users (who don't care about hardware).
I think the oligarchs are happy with this setup:
Apple - Premium
Google - Mainstream (mobile)
Linux - Hobbyist
Microsoft - Mainstream
I expect Microsoft to lose users because not all Windows 7 users will make the jump to 10. But in essence what you see above is what it will look like for the foreseeable future.