What I meant for instance is a mask that is based on curvature or hard edges. This mask isolates areas with hard edges, then you can use the smooth filter to only smooth that area. Like in Maya when you add edge loops to smooth certain parts more than others. So I guess some just common use masks could be nice. In this case maybe it can determine edges at a certain angle and mask only the voxels at those hard edges to smooth. I know subD and voxel are not the same of course but the idea of what to smooth and what not to smooth is what I am getting at. Anyway the implementation you have provided is great!
