> A data URL in an XML instance document
exposes the recipient of the XML to the risks described above. Namely,
link filters can be circumvented and undesirable data can be smuggled in
without notice.
shrug, I don't think those risks are particularly the result of anyURI. If you interpret any XML you get from anywhere it's up to you to ensure that that interpretation is safe.
If it was encoded as a string <base64image>wAARCADqATkDASIA....</base64image> then there are no URI involved but you still have to decide whether or not it is safe to decode the base64.and do something with the result.
David