URIs for user defined simple types

I note that RQ-23
http://www.w3.org/TR/2003/WD-xmlschema-11-req-20030121/#N400183
is a desiderata rather than a requirement.

However, the lack of URIrefs for user defined simple types presents 
substantial difficulty for the use of XML Schema datatypes in RDF and OWL.
I suggest that either RQ-23 be raised to a requirement, or a new 
requirement of URIs for simple types is added.

Jeremy Carroll
(private capacity)