A mere protocol will never "hit the bigtime" without some compelling (non-protocol) reason. It's unfortunate that businesses choose to build silos time and time again, but that's where we are - it's not an issue that can be solved at the protocol level.
Should this be fixed (e.g. through regulation), XMPP is absolutely a sound choice - given, as you say, its 20 years of experience, evolution and deployment track record.