Correspondence from NHD National POC: 

> Our current list of tools work with ARC 10.5.1. Developers are working
> on moving to 10.7 and hope to have that completed by the end of the FY
> which is in October, but that is a floating deadline for sure.

Seems incredibly limiting, now that makes me curious the difference in difficulty between maintaining an ArcGIS utility vs for instance Python packages. Seems even Python packages maintained by only a few contributors manage to stay pretty current. QGIS here I come! 

Additionally I asked if this update would assure backwards compatibility to which I received this response:

> … I don't believe that we support them going backwards in versions,
> but that doesn't mean that they wouldn't work.