[mynameislegion]

Sorry, you haven't thought this through. As long as XMPP exists in a state where there are public servers with varying XEP support then adoption rates will always languish. A user would actually have to do considerable research to understand why features they've come to expect from centralized IM aren't working should they happen to choose the wrong server or client. Without a large degree XEP parity, XMPP has ZERO chance to ever compete with centralized IM. The average user simply won't put up with it.

Matrix has a shot because it's consistent right now. If they stay consistent, they will have an even larger shot.