I’ve begun to wonder about this question. There’s nothing implied in the existence of the fediverse that it will include every site, and there’s nothing implied in the existence of every non-fediverse site which would stop them from forming their own fediverse. One could technically say email providers have already achieved this, though this only really applies to email providers which doesn’t make it as useful as the fediverse we know and love. Are there actually other fediverses out there?
There are hundreds of other federated systems, yes.
As per what your question is asking, I’m not sure if there are fedoverse systems branched off from the “main” one. I guess Lemmy/forum stuff can’t really federate with Microblogging-style things.