What you refer to is called 'transport',such transports for xmpp exist for more than 20 years. They didn't fly because service owners don't really want them to

What you refer to is called 'transport',such transports for xmpp exist for more than 20 years. They didn't fly because service owners don't really want them to. Sometimes services resist actively, sometimes passively. The protocol you use is irrelevant, xmpp, matrix, email, whatever - this is never-ending game of catch up which the service owner will win, because he needs users to use their stock app and all their metadata.