Good explanation Andras.
Yes, we had the voxel grid option in Slicer3 and I sometimes found it helpful, but we ultimately never ported it because turning off interpolation was just as easy, less visual clutter, and more informative. One motivation for turning off interpolation is to understand the partial voluming that comes from thick slices, but personally I would usually leave it off.
@muratmaga - it would be possible to move this from the SlicerMorphRC.py script to the SlicerMorph Preferences as a checkbox, so that users could easily decide which mode they prefer.