A "for comment ballot" may not be the best time to get into details, but…

DiagnosticReport.category is fixed to RAD from v2 HL70074 but this element in the base US Core profile uses an extensible value set which contains a LOINC code for Radiology. As I understand it, the definition for Extensible value sets indicates that the existing LOINC code must be used (although you can use the v2 code in addition). The binding should be updated to require the LOINC code instead.