JSON5 looks really good. I'm not sure about this one part though, from a point of view of simplicity and interoperability when deserializing the data:
> Numbers can include Infinity, -Infinity, NaN, and -NaN.
This is a good thing. It means there is a 1:1 mapping between numbers in JSON5 and IEEE floats.
i've used json5 since the beginning. it's great! just a couple week ago they merged in descriptive error messages too. No more wondering where the bug is!