It's been a while since I last looked at what's cooking at W3C. On first impression, I was surprised to find a working draft called XOP. Does this mean that SOAP attachments are deprecated ?
XOP, the XML Binary Optimization Packaging standard, is an implementation of the Message Transmission Optimization Mechanism (MTOM), and the two are often referred to together (MTOM/XOP). With the release of these standards the W3C is proposing a replacement of the competing WS-Attachments and SwA specifications. Microsoft has already posted MTOM on its specifications page, while previous attachment standards (including SwA) have been demoted to "superseded" status.