First, CDex is focused on Provider to Payer and Provider to Provider exchanges, not payer-to-payer.  (Payer to Payer is covered by the PDex IG.) Second, the hierarchy of systems within a particular provider environment is outside our scope.  FAST is dealing with registries to help discover the appropriate endpoints to use for particular types of searches.  OIDs will almost certainly not be a part of this solution as identifier hierarchy and system topology should generally be unrelated.  (Identifiers shouldn't ever change once they exist, while system topologies change on a semi-regular basis. Third, the scope of CDex is focused on FHIR data exchange, and doesn't cover the sharing of v2 or other data (while in principle, CDA, PDF and other types of documents could be returned via DocumentReference as part of the CDex spec, CDex is completely silent about standards around the encoding of these).  There is no expectation for collation of data as part of the CDex specification.