Douglas Crockford himself recommended using comments if you like then piping it through JSMin. Unfortunately the original post on Google+ no longer exists but it's referenced in a HN thread[0].

    I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have
    destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn’t.

    Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all 
    the comments you like. Then pipe it through JSMin before handing it to your JSON parser.

Which of course doesn't help because you could still just add parsing directives into the comments anyway. But as far as I'm concerned that means the spec implicitly allows comments as long as they're stripped out in transport.

[0]https://news.ycombinator.com/item?id=3912149