I think metadata privacy is as or more important than content privacy. An email containing the text "whats up bro" is far less useful than knowing I sent literally anything to a person of interest. That said, I still think PGP does a good job here and should not be dismissed. That said if NIST and other orgs refuse to accept secp256k1 governments and businesses will refuse to implement it to comply with regulations. 

Nostr doesn't need to be the hammer looking for nails. 

If we're talking linking nostr identities to private communication, we need to consider ditching email entirely which i think is EASILY SOLVED WITH NOSTR. Let email play in the corner and be dumb and insecure because Google controls 90%+ of it and we move on.