Time ago someone proposed to use XML as a tool to describe OCCI. As a result we now have the XML description of high order concepts (kinds), and an XSD that binds the way in which such higher order concepts are described. This is certainly a result.
But XML might be useful also to describe low order concepts, i.e. resources, which is a different (though tightly related) issue. We have an example today in the "erocci" discussion. The fact of having a clean higher order description based on XML/XSD wired in the engine does not help us in clarifying an otherwise straightforward detail about the way resources are described. This is because the JSON rendering is certainly useful for practical reasons, but there is no XSD for JSON (at least to my knowledge).
My idea is that having an XSD also for resources (that describes the syntax for resources, not for kinds) would be beneficial: it can be probably derived from the JSON document, but once defined it can be used to automate the validation of XML resource descriptions, and for all those descriptive languages for which an XML mapping exists (JSON included).