TLDR; Thirty years after the advent of the first instant messaging services, we still haven't reached the stage where instant messaging platforms can freely communicate with each other, as is the case with email. In 1999, the Jabber/XMPP protocol was created and standardized for this purpose by the Internet Engineering Task Force (IETF). Since then,
I didn’t know this even existed, thanks for the link! That list of challenges doesn’t seem that unsurmountable though