Had a good coffee chat about this the other day. I'm now becoming convinced that Nostr is most useful as a social layer for Cashu, not for Bitcoin directly. That is to say your keypair's main job is providing a Cashu token lock (you may have a few such keypairs you give out to others who want to lock tokens to you) and Nostr allows social interaction surrounding that use case.

So a kind of chatroom for each p2pk key you hold.