The new MDK (evolution of MLS protocol on top of Nostr) was announced earlier this summer. Introducing Marmot: The Future of Secure Messaging - JeffG
The reference implementation is in rust. Would probably mesh nicely with Grin slatepack sending seeing that MLS hides metadata. GitHub - parres-hq/mdk: Marmot Development Kit
Other Language bindings are planned as well.
Combining something like this with grin slatepacks would give us static messaging addresses to send slatepacks too. Basically something equivalent to venmo / cash app addresses.