I mean, realistically if the fediverse became mainstream they'd still have that, they'd just make their own Mastodon or Lemmy or whatever else instances and most everyone else would defederate with those. If anything I'm kind of surprised they haven't gone to such platforms already, since while you can certainly be banned from individual instances and instances can be defederated from other instances, you cant be banned from the fediverse as a whole and they could always find a group of like minded jerks and make a little collection of instances for themselves