I've had yet another document published in the RFC series: a very short specification (RFC 6993) that defines a way for a communication endpoint to advertise its XMPP address over SIP. This is a bit of supporting structure for the work I've been doing with Emil Ivov and Enrico Marocco on dual-stack SIP+XMPP clients, in the form of draft-ivov-xmpp-cusax (which itself is close to final review at the IETF).