These may be helpful:
VTK/Filters/Points/vtkHierarchicalBinningFilter
VTK/Filters/Points/vtkExtractHierarchicalBins
Ken Martin used these to build a specialized point viewer app PointView. We were getting ~1billion/pts second rendering speed
https://gitlab.kitware.com/ken-martin/pointview
It’s been a while, but we could dig deeper if you need more information.