Hex encoding effectively doubles the size of content.
If the group consensus is to NOT support native binary payloads then I would suggest using base64 encoding, it's more efficient than hex encoding. This opens the door to security issues, especially access control issues. For example, suppose the binary data is a medical X-ray. Energy companies frequently exchange geographic images and other binary data types. Several people on the SOAP list have indicated their desire for SOAP to support native binary data, the ebXML folks have also identified this need.