I don't have a problem with UWP at all. We've seen from the success of Apple/Google that consumers want a curated experience that maintains itself (unified update system etc) and a guarantee of sorts that anything you download from the official store isn't going to trash your machine.
Don't see a problem, even if running apps from outside that Store requires an opt-in, same as Android, as long as the choice is there.
UWP (if done right) isn't a bad idea in itself and I don't have a problem if it is the principle interface layer for the general consumer - but Windows has always been much more than just the curated layer and a lot of people do use it precisely because it isn't that curated experience.