Trailing commas and JSON comments are are already supported in the newer browsers (try the Chrome console for instance).

Fortunately quoteless strings or optional-commas/newline-separator as proposed in Hjson will never fly. They are brittle and ambiguous. Who knows what will this get parsed as:

    {
        a: hello's and hi's have
            'misplaced' apostrophes
        b: ball: a round # and # bouncy object
        c: cakes and
            candy: both have sugar
            # but how do I include a hash at the start of a multiline-unquoted string?
    }