"most json is machine generated and in most cases should never be manually created by people"
Except when sketching out a static JSON file that you'll eventually implement as a real API connected to a database, once you've experimented and arrived at a good structure. I do this a lot. I wouldn't output JSON5 from a live API, but I would use it for sample data in development.
That's fair. My argument is that you shouldn't muddy the implementation of a protocol for debugging purposes. It creates unnecessary complications that then have to be dealt with on either end in software. I think the problem that you are bringing up is more of a development environment around creating good data structures in JSON rather than a pitfall in the protocol itself.
I'm not saying JSON is perfect just providing a counter argument and stating a general belief I have about over complicating thing when a simple companion tool or something like CSON works just as well. CSON or CoffeeScript are good examples because they provide a more pleasurable environment for the developer but at the end up the day compile down to their native JSON or JavasScript respectively. I think we are in agreement in that I dont like the JSON5 syntax should necessarily be what's going over the wire.
Except when sketching out a static JSON file that you'll eventually implement as a real API connected to a database, once you've experimented and arrived at a good structure. I do this a lot. I wouldn't output JSON5 from a live API, but I would use it for sample data in development.