The fact that it ignores other standards may be true but one of the design goals is to do for data transfer what OpenID has done for single sign-on; light-weight, simple, easy-to-implement, etc. Think of the proposal as a best-of-breed of those heavier technologies.To my mind, best-of-breed implies that the old and new are still of the same breed. But, were OpenID to continue down this road, DTP and the existing XML-based messaging stack would be completely separate species with no chance of successful intermixing.
To Do: make some analogy on how whippets and St. Bernards, bred for very different applications over generations of artificial selection, can still interbreed. ...
The same can be said of OpenID as it relates to SAML ...I agree.
Regardless, a comment from Grant Monroe on my original post indicates that the next rev of DTP will ditch XML completely and instead build on MIME and S/MIME. So, it seems this particular concern is moot.