I see advertising for Matrix every single time the chat topic comes up. Having looked at the protocol, it seems massively more inefficient than just using XMPP, which has numerous clients and a lot of features. Can Matrix do anything that XMPP can not?

Note that I have read the claims at http://matrix.org/docs/guides/faq.html#what-is-the-differenc... but critizising the minimal XMPP baseline feature set while claiming that XMPP is not being “well designed for mobile use cases” seems like someone wants to have their cake and eat it too – I have used XMPP over low-bandwith high-latency mobile data connections for years and noticed that XMPP's stream syncronization is a really nice feature for that use case.