appContext is only passed when the launch is triggered by CDS Hooks.  Context information for stand-alone launch is driven by scope requests.  Guidance from the SMART community is that we should have a custom launch context request to solicit "current order(s) or DTR QuestionnareResponse(s) in the user's context - if any".  This context would have a custom URL - for example http://hl7.org/fhir/us/davinci-dtr/smart-app-launch-request.  

The spec should indicate that the resources corresponding to this context (if any) would be passed in the fhirContext element.  As well, the app should also always ask for the launch/patient and the openId and fhirUser contexts.