One of the things I've mentioned there is the need for better testing for protocol compliance; and also the (possibly overdue?) clarification and republication of the v3.1 spec. I think the first is potentially a Paho task, and the second is (currently) an IBM one, since they host the spec document on developerWorks. I'm thinking that the spec update should be a dated, v3.1 revision 2 document, incorporating the discussions we've had in the community over the past year, most of which are collected via http://mqtt.org/wiki/doku.php/mqtt_protocol
containing something else worth adding. If we leak into the "Future Enhancements" section of the clarifications page, we might want to rev to v3.2?