The original notion was that we couldn't count on provider systems being able to store QuestionnaireResponse instances containing the work in progress (or 'computable' final results).  Given that US Core R5 now includes writing of QuestionnaireResponses as mandatory, it seems this limitation is no longer an issue, and it's best to just eliminate all of the complexity of payer-side storage of work in progress. 

DTR should be updated to remove all notion of using DocumentReference to store information on payer or provider systems.  Instead, QuestionnaireResponse instances should be stored only on provider systems (whether complete or work-in-progress).  QuestionnaireResponses can be included as part of PAS submissions or claims submissions and/or retained for audit purposes.