nip-4 and nip-44 are current standard of quality of encryption with ecdh and AES based cryptography

i think it could be made a lot stronger, of course, especially if we start to talk about adding synchronous handshake protocols for DMs (i mean, if someone is currently live in chat, why not?) but we only just finally got broad support for auth which was a prerequisite for anything further involving mediated private communications... i wouldn't be holding my breath on the question of actually decent functionality but the possibility is there and it only takes the partnership of a competent relay and client dev to become a reality 

 the problem is not the crypto, it’s how devs implement it 

 client side of it is a big part of why it's not happened yet

creating a scheme that is decently secure even with untrusted relays that allows multiple devices to sync data properly is not a simple thing, otherwise simplex and session would already have this functionality, and the fact is that privacy comms people in general are quite idiotic about the problem of async and multi-device, both of them are essential to easy and broad adoption