What advantage does that have compared to simple bracket highlighting and indentation? Editors can easily highlight mismatched parentheses, they are however rarely smart enough to auto-close XML tag pairs. I just see it as unnecessary clutter.

Meanwhile the only issue I have with JSON is the lack of support for trailing commas.

Named closing tags are another confirmation when inserting stuff at the end. I think multiple different confirmations can be easier to recognize than a single one.