Steve, I spoke with Spiros and he straightened me out. The fancy hashing and threading we did is in vtkGeometryFilter and, yes, is much faster. The original (serial) hashing concept was originated by Charles Law in vtkDataSetSurfaceFilter but has been mostly left relatively unchanged because it has the ability to handle non-linear VTK cell types. vtkGeometryFilter will actually delegate to vtkDataSetSurfaceFilter if it detects non-linear cells. So yes, please create a MR to swap the filters as vtkGeometryFilter should be a drop in replacement. Obviously in the future we should consolidate the classes, but it seems we’re all busy 
FYI as a workaround, I explicitly use a vtkGeometryFilter + vtkPolyDataMapper in the pipeline.