That's the issue though. It doesn't introduce anything useful in terms of replacing JSON (it can even make things worse), and for other uses better solutions already exist.

The fact that in theory if it was magically supported everywhere, it might be serviceable is neither her nor there. It's not useful information. It's not gonna happen because there's no reason to switch from JSON to this, and many reasons not to. Likewise, for other applications there are better solutions.

People started using JSON even though at that point it wasn't standard because it had real benefits over what they were currently using. There isn't any situation where using this would provide a real benefit except to satisfy personal whims, and it would have the drawbacks listed.