Spec seems to be a bit of a mess
It doesn't help that its an extension to XMPP, which is not the internet's simplest protocol.
The authors assert the success of email was due to open protocols. I'd argue that the success of email was largely down to being a very very very simple and easy to implement protocol. SMTP sits directly on top of TCP. It uses ASCII. It uses half a dozen commands. That's it, it's simple enough to "implement" by hand, using telnet. No need for fancy API's. You could teach a ten year old to do it.
Wave uses XMPP, and this sits on top of TCP, TLS, and SASL, using XML, UTF-8, X509, MD5, base-64, URNs etc, which is great - much better than email - but has a lot bigger learning curve. You need libraries and APIs, frameworks, public key infrastructures, XML parsers, and so on. On the server side, I wonder if we will ever see the situation where practically every organisation on the net has an XMPP server and they communicate seemlessly (as we see now, more or less with SMTP).
Or will the complexity lead to a few big walled gardens like Facebook and Twitter?