The current FHIRcast specification is linked to FHIR version R4b. In the pull request related to FHIR-40658, it is proposed to move the FHIR version to R5.

FHIRcast is currently deployed in situations where R4 and R4b are the norm (US - linked to US core). IHE is standardizing on R5. This requires FHIRcast to handle FHIR resources of multiple types.

In the past this was not an issue as the changes between the different FHIR versions did not effect the elements specified in the _elements field of the event-definition. This has changed in R5 as the accession number and study instance uid location in an ImagingStudy have changed.

In my opinion, this requires FHIRcast to support multiple versions of FHIR.

I propose that we change the specification in the following manner:

1. Add definitions of the resources in the events for all current FHIR versions (R4,R5, R4b). All new FHIRcast events must specify resource profiles for R4, R4b and R5.
2. Make the hub linked to a specific FHIR version - add a field to Conformance that states the FHIR version of the event.