The best comparison is between Mastodon and Nostr. Both are also separate networks that officially do not communicate with each other. However, there is a fully functional 'bridge', which allows you to follow people (and comment etc) who are on the Nostr network directly from your Mastodon account, and visa versa.
I'd expect something similar to happen between Bluesky and the fediverse as well.
Great question btw, and sorry for the long answer haha