Like, practically speaking, when we say "take the useful parts of Bluesky's experiments and port them over to the Fediverse" what I think people mean in practice is "port them over to Mastodon”.
I really don't think there is a Fediverse (i.e. an underlying network-of-networks speaking a common protocol of which Mastodon is _one_ application). There's just Mastodon. That's it.