Earlier quoted context omitted.
What do you mean, 'xmpp practically doesn't interoperate with anything'?! Dozens of thousands of xmpp servers interoperate and deliver messages to each other. Or do you expect it to interoperate with Telegram? What next would you expect, UDP ICMP interoperability?
There are in fact transports for Telegram on the XMPP network. https://jabber.hot-chilli.net/server-specifications/#Transpo... https://www.jabbim.com/home.html
Moreover, I came to a conclusion that reliance on transports reinforces the network effect of external services and weakens XMPP's network effect. Do not use them.