I think the cat’s out of the bag. There’s no stopping it at this point. And even if ever person who runs a Mastodon server got together to push back, defederated with Threads and BlueSky, and tried to stay away, it wouldn’t even be a blip on the radar for these big players.
To be honest, I’m not sold on federation in general for social media. I think it’s an answer to the wrong question. We’re asking “how can we make social media better?” and not “why do we need social media at all?”
Federation has shown itself to be extremely problematic. You have people coming and going from other instances that you don’t control and can’t enforce in any way other than to just block the instance. If I have e.g. a Mastodon instance based around a safe, positive space for the queer community, and others have instances based around bigotry, white supremacy, transphobia, etc. (which they do), then I either allow bigots to come and go, or I have to spend an inordinate amount of extra time on moderation. Same goes for Lemmy/kbin/etc.
People are also continuing to think with a limited frame of reference. The idea of federation is still “how can I get all my ‘content’ in one place?” because we’ve been dominated by these monolithic walled gardens for the last decade. Sure it might be annoying to have to have multiple logins for difference services, but I’d rather that over having a single place where Nazis can come and go as they please with few to no tools to stop them.