This "JSON5" thing is an abomination. Use whatever quotes you like! More string escaping rules! Adding these things would make JSON worse, not better.
Here's another idea: why not write a tool that tidies up your hand-written JSON files? You could even re-use your "JSON5" parser to do it. That way you can be as lazy as you like when writing files, but not expect the rest of the world to learn your new dialect.