Nostr can be private if you encrypt it, in fact you can be sure its private since its verifiable on public infrastructure, Formstr responses are already encrypted. 

Cooking up an update for private access controlled forms as well.   

 And you can avoid metadata leaks if you use giftwraps, before anyone comes up with that as an excuse to not use nostr.  

 Nostr dm encryption is not secure 

 Break nip44