That's kinda what we are trying to build. A local interface that every app can use. Because the current path is every client connecting to the same relays separately
Discussion
Yes, the Relay Interface is the protocol. I would aim to shift all this behind one side or the other of the Relay, rather than establish another interface or platform-specific standard, this early in NOSTR
Relay Extensions and additional ports and features negotiated via handshake would be a better target for us to aim towards.