Hah, no, XHTML wasn't an "efficiency", but you're also asking for a rigorous standard.
I'm still against a binary standard. It makes novel clients much harder to write, and the fundamental gains are small. I've personally written code that completes an HTTP POST with a JSON payload in less than a millisecond... if you want performance there are ways to make that happen without locking out casual developers
TCP is binary. TLS is binary. QUIC is binary. Casual developers are not locked out of them.
If a developer is casual, they won't care about the binary details. They will just call a function and get a JSON blob out of it. I think the insides can be binary and the API can be JSON and we can have both.
No application binary implements TCP. I can assure you that only environments with an SSL or QUIC library will ever use those protocols. Maybe nostr is necessarily the same because of event ids and cryptographic signatures? It's possible, but I'm not immediately convinced
