Member _vtk_module_add_header_tests (): Move this function out to be VTK-specific, probably into vtkModuleTesting.cmake. Each module would then need to manually call this function. It currently assumes it is in VTK itself.
Member vtk_module_add_python_package (name): Support freezing the Python package. This should create a header and the associated target should provide an interface for including this header. The target should then be exported and the header installed properly.
Class vtkPVMergeTables: We may want to merge this functionality into vtkMergeTables filter itself.
Class vtkPVMergeTablesMultiBlock: We may want to consolidate with vtkPVMergeTable somehow