Not all systems in the US that have to interact with the healthcare system are clinical systems. Requiring Must Support on DocumentReference.category:us-core slice that has a required binding with only one code of "clinical-note" is very limiting. 

This means that systems that address areas outside of the traditional clinical setting cannot be conformant to US Core DocumentReference. This includes patient facing/focused applications, systems that deal with medical legal matters, and human service organization systems to name a few. 

This is problematic for Advance Directives, Medical power of attorney, and human services (provided by Community based Organizations).