It should be possible to launch a smart application (or URL) using a Task (see https://jira.hl7.org/browse/FHIR-28681 and https://jira.hl7.org/browse/FHIR-36319).
CDS should define a profile and example that shows how this could be done. When such task is defined, one should also define a profile to launch Questionnaires.

This would allow CDS hooks PlanDefinitions and CDS Services to request launch of applications as a Suggestion or system action.

Such profile definition may look like the shorthand samples below.

Profile: CdsTask
Parent: Task

• code 1..1 MS
• code from CdsTaskTypes
• input 1..*

Profile: LaunchAppTask
Description: "Defines a Task that indicates the user should launch an application."
Parent: CdsTask

• code 1..1 MS
• code
• coding 1..*
• coding[0] = CdsTaskTypes#launch-app
• input 1..*
• input ^slicing.discriminator.type = #value
• input ^slicing.discriminator.path= "coding.system"
• input ^slicing.discriminator.rules = #open
• input contains apptype 1..1
• input[apptype].coding 1..*
• input[apptype].coding from CdsApplicationTypes (extensible)
• input[apptype].value[x] only url

Profile: LaunchQuestionnaireTask
Description: "Defines a Task that indicates the user should launch a Questionnaire."
Parent: CdsTask

• code 1..1 MS
• code
• coding 1..*
• coding[0] = CdsTaskTypes#launch-app
• input 1..*
• input ^slicing.discriminator.type = #value
• input ^slicing.discriminator.path= "coding.system"
• input ^slicing.discriminator.rules = #open
• input contains questionnaire 1..1
• Input[questionnaire].coding 1..*
• Input[questionnaire].coding = CdsTasksCodes#launch-questionnaire
• Input[questionnaire].value[x] only Reference(Questionnaire)

ValueSet: CdsApplicationTypes
Id: cds-application-types
Title: "Application launch types"
Description: "Defines mechanisms to launch applications".

• CdsTasksCodes#smartonfhir-application "SMART on FHIR application URL."
  "The URL of a SMART on FHIR application."
• CdsTasksCodes#web-page "Webpage URL."
  "The URL of a webpage."

ValueSet: CdsTaskTypes
Id: cds-task-types
Title: "Tasks to perform typical CDS tasks."
Description: "Defines codes for Tasks typically used in CDS deployments.".

• CdsTasksCodes#launch-questionnaire "Launch Questionnaire"
  "The task suggest launching an questionnaire"
• CdsTasksCodes#launch-app "Launch Applications"
  "The task suggest launching an application"

CodeSystem: CdsTasksCodes
Id: cds-tasks
Title: "CDS Task types"
Description: "Codes used to indicate specific task types used in CDS context."

• #launch-questionnaire "Launch Questionnaire"
  "The task suggest launching an questionnaire"
• #launch-app "Launch Applications"
  "The task suggest launching an application"
• #smartonfhir-application "SMART on FHIR application URL."
  "The URL of a SMART on FHIR application."
• #web-page "Webpage URL."
  "The URL of a webpage."