Interoperability between these systems should be a public policy goal. I don't have to buy an AT&T phone anymore to call my friends; not sure why I have to buy iOS to chat with them.
I agree with you but this is a problem that date backs to the 90s (anyone remember Bitlbee, Trillion, Pidgeon, etc?). Unfortunately incompatibility is seen by businesses a feature rather than a flaw -- despite the annoyances it causes for users.
There's been a few open standards. The problem isn't that standards exist, it's that walled gardens are generally more profitable.
In fact Google Talk, Facebook Messenger and Skype were all either based upon, or supported XMPP...and now don't. Slack used to support IRC and not doesn't. There's a term often credited to Microsoft that also applies here: embrace, extend, extinguish.
I don't mind the interoperability. Take email for example. Even if you avoid Gmail/Google, so many people do, so Googs eventually gets your email anyway. So we chat, even if you don't use FB, if someone you chat with does, they still get that conversation. So the interoperability provides a buffer or insulator between you and the company you are wanting to avoid.
Then again, I've kinda given up on email privacy since at least half of my emails go to Google's servers anyway. I'm not sure if we can avoid Facebook having my IP address (or whatever future attack vectors are found after the protocol has been standardised) if I message WhatsApp users from my Signal account.
Interoperability is tricky when one set of apps has end to end encryption as a requirement, and the other set has absence of end to end encryption as a requirement.
