[davecridland]

Matrix will hit exactly the same problem in a few years. The solution is certainly not to restart with a clean slate every few years and fucks to you if you wanted compatibility. That's Google's approach, where every few years they trash an old service and - maybe - replace it with a new one that works in a different way.

There's no simple answers to this. I can tell you it's absolutely not a protocol issue - the protocol issues are ensuring graceful degradation remains possible during advances, which XMPP does well - but a political one. Profile specifications, which indicate groups of XEPs which the community expects to be supported, are part of this. Certification might also need to happen. Maybe monetary awards, even.

One of the biggest things currently driving server implementors to get the XEP support, and server maintainers to deploy it, though, is folk like inputmice driving the market with Conversations.

[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.