@Martti Malmi last year I wrote this, but didn't have time to implement on a proper client: 
Maybe it can be useful on building a totally private communication.
It encrypts all the metadata, uses ephemeral key (like you recently implemented on Iris, and a kind of channel mixer.
It has some interesting ideas that can be used.
GitHub
GitHub - eddieoz/nostr-stealth: Built on top of the Nostr protocol, specifically designed to ensure sender and receiver metadata full anonymity. Leveraging the concept of channels (or mixers), Nostr-Stealth ensures that individual messages between users cannot be distinguished or differentiated, thus enhancing user privacy.
Built on top of the Nostr protocol, specifically designed to ensure sender and receiver metadata full anonymity. Leveraging the concept of channels...
