That’s in some sense getting back to the “open protocols” idea of ~2005, with federation and common identities. You’d still have 1) bothersome process of maintaining such a site, 2) problems how to find such, 3) an identity provider which can go down with your identity, like a Lemmy instance can.
It’s insufficient. Facebook and others have used an existing demand for a recommendation system and automatic moderation and search and all this junk.