We got a NIP!

https://github.com/nostr-protocol/nips/pull/1222

The NIP covers UDS communication more generally. I wrote a reference implementation in Rust that uses JSON-RPC 2.0 requests/responses wrapped in NIP-04 events exactly as described in NIP-46:

https://crates.io/crates/nip-55

The crate comes with a very basic NIP-46-over-NIP-55 module:

https://docs.rs/nip-55/0.3.1/nip_55/nip46/index.html