HD keychains do this with a whole keychain. you can just do the same thing. seed key, path /identify /encrypt. then you can chain those as well. you can do xpubs. we haven't even touched what we could do with this. nostr identities become hd keychains with different derivation paths for different roles. revocability is not given in this but rotation can be done every time by marking the message with a tag. so even if one message is revealed, it is tagged, and only that tag is breached. i think this is called forward secrecy. anyway. *yawn*

Yes. Treat the auth key like identity and the encryption key like luggage. Losing one should not nuke both your social graph and your DM past. Key monoculture is cope.