JSON5 is also meant to be language-agnostic. It derives its syntax from ES5 in the same way that JSON derived its syntax from ES3.
I'm aware that JSON is final — it's my hope that a new format that's easier to write (whether this or something else) picks up steam — but thanks for the feedback on the name! I consciously used a different file extension (.json5) to avoid conflicts; hopefully that's a good start.
I already use (and love) CoffeeScript, but my motivation for building this was to have tools use it natively, so that sibling files in a different format wouldn't have to be maintained alongside the needed JSON.
1) to be language agnostic. Following ES5's syntax directions is fine for ES5 focused development, possibly not for others.
2) to be final - i.e. there is no version number. If you want to extend or build something else, I am fairly certain Douglas would prefer that you call it something else. See http://inkdroid.org/journal/2012/04/30/lessons-of-json/ at 5:30 in the video.
Don't take these points as criticisms, I too would like to be able to use single quotes and trailing commas and everything else here. I think though that in order to work with JSON as a static spec, an alternative approach could be to have your project be a layer like HAML, SASS or CoffeeScript. Each of those tools compiles or transforms to conforming input for their target specs rather than replacing them.