I want to emphasize that I was not thinking about JSON RPC as a specific protocol, but more as a JSON format to transfer data, similar to how REST APIs usually do, and some kind of "HTTP method agnostic remote procedure call", it does not have to be JSON RPC standard.
Personally, I am a fan of just having API Class-es + methods that automatically map to API calls with automatic api interface and doc builders. I find that it would be super strange if I had to prefix my internal methods with DELETE or PUT based on do they remove or add to some Array. Using that logic, why do that in APIs.
I just find it super strange that people want to mirror their app logic + error response codes to some protocol like HTTP – ridiculous :) Why not go even lower as TCP and use some of that spec for our client <> server API conn. Many people will laugh, but if you think about it, where is the difference?