Which is fine, ActivityPub is an open protcol. You don't even need to cleanroom, its all there. The AGPL is a shield against corporate interests, given how things are going that's a much needed feature.

That's not the end of the world, though it does mean that a competitor could always start using it. I was going to say just use Lemmy but a major site would probably want to have their own fork for stability so they're not at the whims of someone else.

They could probably use an open fork for a while while also developing their own software that would be compatible and then seamlessly switched out.