Oddbean new post about login | logout The reason why signal is so popular is easy and reliable asynchronous comms. I don't believe you can achieve this with a p2p stack. At least with a signal-level ux.
Could it be part of the protocol that relays only send encrypted messages if they know the person receiving is the intended recipient? In that sense the relay is behaving more like a private server and should solve any privacy concerns.
I feel this should be pretty easy to do (theoretically at least), when you ask for DMs prove ownership of your private key and then the relay only responds with DMs sent to the corresponding public key
Looks like this is pretty much the proposed NIP-21 I guess