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.