Not quite true. Just because JSX resembles XML, it doesn't mean it can only output XML. Plenty of non-XML render targets exist for React: canvas, terminal, Sketch (I believe the file format is JSON).

The primary restriction is that your output can be modelled as a tree in some way, and what you find is that nearly everything falls into this category. I don't know if anyone's done it yet, but a plain-text renderer is certainly possible, I imagine it would be very similar to a terminal renderer.

If you're saying that JSX can do more than XML because you can transform from XML into other things, then yes, that's trivially true.

No, I'm saying that JSX isn't XML, it just very loosely resembles it. It can't even naively output XML because it (currently) mandates a single root node, and XML has a doctype node as a sibling to that.

JSX transpiles down to a tree of function calls, it's literally nothing more than that, the only time it might be considered XML is in the final rendered content. Syntactically, JSX isn't even valid XML.