Especially for those of us who don't work in games, it's really handy to paint on a surface that will more closely approximate the limit surface at render time. In Mari for example, we often have to import a highly-tesselated mesh. And that's okay, especially if we decimate it in Zbrush first, but in the case of mesh with less sculpted complexity, we could really benefit from painting on a smoothed, non-cage, subd mesh.
Would be great to have way to toggle the mesh's subd level (0,1,2..)...
Or perhaps you're planning on implementing OpenSubDiv...?