I find that the "unnecessary features" and footguns are what makes XML, well, XML. I guess there must be some legitimate usage of those, or at least was back in the day. If you strip them out, you'd end up with a JSON-like (so you may as well use JSON).
No, you would have an extensible markup language. And json is not a good fit for markup.
Now, xml has also been used for a lot of things where a hierarchical format like json would have worked better than a markup format, of which SAML would be a good example. But there are also cases where a markup format makes more sense, like svg or docbook, or odf.
