I especially like the section on consistent terminology. The real world space and desk/filing metaphors used for online stuff in other applications suck.
I'm torn, because on the one hand, yes! — the hour I spent figuring out which PGP XEP was the right one is an hour I won't get back. But, "only the XEPs you need to implement for a modern messaging application, ignoring historical cruft and excessive backwards-compatibility" sounds so much like the beginning of an extend-and-extinguish cycle.