Will define a standard extension on QuestionnaireResponse for capturing this information, mirroring the structures and leveraging the same data types, cardinality and value sets). Will raise the question on Zulip as to whether the context for this extension should be extended to other event resources (and perhaps others such as CarePlan).  If there's a desire to broaden the scope, we'll extend the context. Will expose the extension in SDC as optional (mustSupport=false).