JSON5 is elegant in that it's purely a subset of JavaScript (exactly as the original JSON is). But in practice that doesn't really gain you much besides a familiar syntax, and Hjson looks simple enough that the slight differences from JS shouldn't be a problem.
The real problem is how to persuade people to use something like this. For the few cases where JSON isn't already entrenched, YAML and TOML and the like have already salted the earth.
I prefer explicitly marking strings. If I try to write a number, I want confidence that I'll get either a number or a parse error. (Though that doesn't necessarily mean quoting the string, other methods could work.)