Steps to move forward
- Make all filters that accept only vtkMultiBlockDataSet to accept vtkPartitionedDataSetCollection too
- Make the pipeline optionally convert sources/readers/filters that generate vtkMultiBlockDataSet to generate vtkPartitionedDataSetCollection
- Change the guts of every source/reader/filter to generate only vtkPartitionedDataSetCollection instead of vtkMultiBlockDataSet
- Deprecate vtkMultiBlockDataSet
Steps 3/4 are breaking changes so hopefully they will make it in VTK 10.