The latest Rhino WIP (Tuesday, December 10, 2019) has two kinds of SubD point editing.
Use the PointsOn command to see and edit SubD vertex control net points.
Use the EditPtOn command to see and edit SubD vertex surface points.
The attached SubD point editing.3dm file is a short tutorial to get you started.
SubD point editing.3dm (102.4 KB)