Yeah, funny you picked up on the derived IDs for groups. I talked about that with  nostr:npub1klkk3vrzme455yh9rl2jshq7rc8dpegj3ndf82c3ks2sk40dxt7qulx3vt earlier today. I think that's mostly a client implementation detail instead of a protocol level thing but it's a cool idea to make it harder to triangulate on the size or membership of groups.