" (Note: This could be a searchable Adaptive Questionnaire that just provides the next-question operation URL.)"

Remove this line.  An adaptive Questionnaire will be returned as a Questionnaire that complies with the 'adaptive' SDC profile - which contains an extension indicating where to call the $next-question operation.  There is no ability to return a choice of a resource or a URL, and we wouldn't want to anyhow as the metadata about the Questionnaire might still be of interest for display.