There's a reason why this went from widely supported/used to... not so much. And even if most people claim it's big-co's locking down their ecosystems (which is partly true), the "extensibility" of XMPP allows for a very convoluted ecosystem with some servers supporting certain XEP and some not. Also, sorry, but XML just sucks to work with nowadays :(
No one hand codes JSON. No one hand codes XML. It's much of a muchness.