You can’t really “fork” nostr. Not like you can fork bitcoin.
I guess you could say there are lots of “forks” already, with different people experimenting with different NIPs. But guess what? They’re still (mostly) interoperable. Unlike something like bluesky, which is more like bitcoin. Change one tiny detail and you have to build your userbase from scratch. No interoperability whatsoever.
This is one of nostr’s greatest strengths.