Most sites are not going to implement this themselves. I think they're in prime position to become a key broker of identity in the same way that a lot of people already log in with their meta or google account to unrelated websites. They become very entrenched and get a ton of data that way.

As more and more people essentially lock themselves in with these identitybrokers tho I imagine it has a very stifling effect on speech tho. Imagine getting banned from those.