The nice thing about JSON5 is, you can move a project from a JSON-based config to JSON5-based config and get a significant improvement in human friendliness without sacrificing backwards compatibility; yet it's a fairly well-documented and well-known format that's not as clinically insane as YAML. It's interesting to see how many people in that HN thread talks about JSON5 as if it's a data interchange format, complaining about things like comments and other features not needed for data interchange, when it's clearly meant to be a format for humans to read/write for things like configs (or they pretend all the problems with hand-editing JSON is trivially solved in the text editor).

I do have a few gripes though. I think allowing so many weird Unicode characters as whitespace was a bad choice. JSON5's reliance on Unicode character classes in general both makes it harder to write a parser and introduces compatibility concerns as different parsers will parse files differently based on which version of Unicode they use. But all in all, JSON5 is pretty nice.

In fact, I recently wrote my own parser for it: https://github.com/mortie/json5cpp.