I was thinking of what nostr is. The initial concept I had was that nostr is a specific client-server (relayed) protocol for social network defined as NIP-1, plus extensions on top.

Now tend to see nostr is some other way. Nostr is the way of producing public authentificated data feeds by pseudonymous web-of-trust identities. NIP-1, existing relays etc are just current implementation details, which may change. What would always remain are the data feeds linked to decentralized identities.