I think the real problem with XMPP (and the visible lag between state of the art and specifications) is that there's no single big vendor behind it. It's both a pro (in that the specs should accommodate what the community wants, not what the vendor wants) and a con (because specs are written when vendors feel like it).
An interesting example is Google with SPDY. They wanted something new, built it, tested it, and then wrote the specifications (along with other actors of course). I think it is fair to say that without the SPDY experiment we wouldn't have seen HTTP/2 coming so fast. Google and the other actors had enough incentive (and actual time and money to spend) to make it go further. In the case of XMPP there's no such actor, unfortunately.
Yeah, good point. USB-C wouldn't have ratified so quickly if Apple didn't hand it over [1]. Apple could also be credited with putting pressure on OpenGL to release Vulcan when they released Metal API a year prior. Before this, OpenCL/GL hand't changed drastically in years. It seems big companies are involved whenever positive momentum happens.
An interesting example is Google with SPDY. They wanted something new, built it, tested it, and then wrote the specifications (along with other actors of course). I think it is fair to say that without the SPDY experiment we wouldn't have seen HTTP/2 coming so fast. Google and the other actors had enough incentive (and actual time and money to spend) to make it go further. In the case of XMPP there's no such actor, unfortunately.