How will screenreaders do this?No one can see into the future and see what's happening. But you shouldn't be fearful about this. In different post I could read that Microsoft Store isn't as successful as for example the Apple Store or Google Store. Vendors have to pay money to publish their apps in Microsoft Store and not all of them are willing to do this. And even if there's only one App Store to download apps you can be sure the screenreader companies will adapt to this situation. But this is far far away, at least to my opinion.
Further you wrote:
Another good reason to lean more towards Linux.As far as I know it's hard to deal with Linux as a blind or visually impaired person. I won't say this is impossible but to my opinion you have to restrict yourself in using Linux. Maybe a Mac could be an alternative for you - I know a view people using it or using Windows and a Mac at the same time (me too).