I agree, especially in regards to the comments, because sometimes the data itself isn't enough and additional human-readable context can be really useful!
In that regard, JSON5 is a wonderful idea, even if sadly it isn't widespread: https://json5.org/
It also supports the trailing commas and overall just feels like what JSON should be, to make it better without overcomplicating it.
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.