The trouble I can sees having is that they'd just lose the younger generation, who they already are due to smart phones. They'd make even less reason for youth to own a Microsoft device and pay the sub, and then as they learn to live without windows, it reduces the likelihood of them ever even trying it due to the cost. Then it'll just be the old adults the stick with it, each year getting older and older and slowly dying off, and the future use something else.
If not for work, I know very very few people that use a desktop pc, a small amount have laptops but haven't switched them on in ages.
Imagine telling those users they need to pay £7 per month to have the operating system.
Ms could easily now bundle xbox game pass, Microsoft Office, and windows os into one £10-£15 per month cost, perhaps £20 p/M for a family plan getting 5-10 devices or something.
When I was a kid, my parents bought us all a pc one year, 6 kids a brand new pc, was crazy but we were lucky as it got us ahead and learning young. I can't image telling those parents, on top of buying the pc, you have to pay £35 per month just for the operating system.
With that said, maybe there will be a completely free bare bones home version