There is a new spec, or to be more exact, a new working draft of a spec available at W3C: The SOAP Message Transmission Optimization Mechanism.
It must have got something to do with serializing SOAP messages in a more efficient way, but either I'm too dumb or it's too late for me to make much sense of it. There is also a slight probability that it simply is a badly written spec, but who am I to say ...