This issue arose in the development of the Plan-Net (Provider Directory) IG – http://hl7.org/fhir/us/davinci-pdex-plan-net/ whose purpose is to define a FHIR interface to a health insurer’s insurance plans, their associated networks, and the organizations and providers that participate in these networks.
USCorePractitionerRole.practitioner is constrained to 1..1 (in R4, it is 0..1).
Key stakeholders in the development of the PlanNet (and historically, the VhDir IG on which the Plan-Net design is based) are the DoD and VA. A requirement that came out of VhDir and is addressed by Plan-Net is the ability to represent in the directory a role for an individual where the specific individual assigned to the role at any particular time is not known in advance. For example, a cancer clinic could have an Internal Medicine Physician role (that could be queried through the API), but the particular physician in the role at any given time is not recorded in the directory.
In Plan-Net, PractitionerRole.practitioner is constrained to 0..1 (as per R4), and an invariant is added requiring that at least one of organization, practitioner, healthcareservice, or location be provided.