Considering the interest to use this guide for certification, we need to more clearly recognize the interactions between systems than only "provider" and "payer".  For CRD that means there is an initiating system (e.g., EHR, PMS, Sched, etc.) that interacts either directly with a payer's CRD HIT, or with an intermediary (e.g., SMART App) that in turn interacts with the payer. 

Therefore there is the interaction between the initiating system and the SMART app using CDS Hooks, access to FHIR US Core based APIs for additional data, and a notification on the disposition of the requirement determination.  In between the SMART App interacts with the payer using similar CDS Hooks, something to address additional data requests from the payer that are then translated into FHIR US Core calls, and ability to notify the initiating system. 

Note there is an alternative way to lower the entry for initiating systems and that is to have a simple, non-CDS Hooks launch where the SMART App queries the initiating system using FHIR US Core + Coverage resources.

Even though some of these interactions may be formatted the same, having clarity on the more granular roles at a system level will add the definition of certification requirements to avoid any ambiguity on what parts a system must support at a minimum.