XML is fast becoming the de facto standard for business to business transactions. HIPAA is based on EDI. Do you expect in the near future to allow XML transactions as well as EDI?
At present, certain X12N and NCPDP EDI standards have been adopted as HIPAA standards. If these groups (or other ANSI-accredited standard setting organizations) develop XML-based standards that the industry would adopt, DHHS would consider adopting them as the HIPAA standards.
Note that the regulations (at 162.940) allow for pilot testing of proposed modifications. A group wishing to pilot test an XML-based transaction could apply to the Secretary of DHHS for permission to test that transaction.