Based on discussion with Gino, the Task is behaving more as a 'to do' than an 'authorization' and linking Task.output to the QuestionnaireResponse is viable.  That's the preferred mechanism for establishing a link.  Also, in R4/R5, that's the only thing that's possible. While we could add Task as an allowed target of Questionnaire.basedOn, we feel this would possibly result in confusion about how to link the resources or result in bi-directional links.  Therefore, we would like to wait until there's a use-case where Questionnaire.basedOn is the only appropriate link (and Task.output pointing tot the QuestionnaireResponse wouldn't be appropriate/feasible).  If there is such a use-case, please resubmit the request with more justification.