I like the idea of JSON5, but it allows a bit too much in my opinion. For example, why add the single quote? Why hexadecimal identifiers?
https://nigeltao.github.io/blog/2021/json-with-commas-commen... https://github.com/tailscale/hujson
But if you did want to fix JSON, the yes, trailing commas and comments are the absolute minimum bar, but single quote is actually probably the the third absolute must-fix.
The reason is just that so much JavaScript tooling is now configured to autoformat code (including the JSON bits) to swap " to ', thanks in large part to Prettier (which also should almost never be used, sigh, but that's a topic for another HN bikeshed...)
hexadecimal identifiers, yeah, nah
I'm curious what you have against Prettier.