Whilst I agree with you, there is nothing stopping someone defining link structures in JSON documents, coining a new media type e.g. JSON+Link and boom, problem solved.
Well, I'm responding to you and to your siblings. You're right. You can create a new MIME type and the problem is solved. Fortunately, as the sibling comments pointed out, there is an extension. What I want to see happen is that the JSON + Links becomes a standard. Ideally a W3C. Otherwise we're into the old XKCD comic https://xkcd.com/927/