Transitioning Federated HIE from XCA to FHIR Query

I already have one proposal for the transition from the current Federated Health Information Exchange to supporting FHIR, that is based on a transition from CDA to FHIR-Documents. In that proposal, I make it clear that this is NOT an end-state, but rather a method to more smoothly transition. A key point of a smooth transition is that it does not stop what is working today, but provides methods of supporting the future for those early adopters. That proposal recognizes...