The only 2 things I'd like to add in JSON are trailing commas and comments, and this is already supported in most JSON configs (.eslintrc, .babelrc, ..), it's called JSONC I believe
I kind of wish Apple hadn't deprecated NeXT-style property lists and had instead gone in the direction of GNUstep by trying to improve the classic format.
Note that that page forgets to actually make an argument against unquoted keys.
The "Why not JSON5, JSONC #1, HJSON or HOCON instead?" answer says it's because of "unquoted strings", then links to a section that only talks about unquoted values. JSON5 doesn't have unquoted values.
