I'm not saying Nostr could fill the function they strive for, but there are some overlap. Key handling -- Nostr has infra for key storage, signers, etc. 'Home servers' - light server which you can (and should) run yourself for Pubky -- maybe Nostr relay infra could do the same.

The DHT lookup, app logic, that's specific and new.

I'd be more sympathetic if there was some kind of synergy between Nostr & Pubky. Looking from a distance, Nostr also has to do with decentralized web/publishing afterall.