The transition to 6.x is not realistic, most downstream projects did not switch to the new version, there are so many API changes....but it would be nice to have a vtk 6 package available in unstable(must conflict with vtk 5).
I will build a local 5.10 package and rebuild all reverse dependencies just to see where we are with 5.10. Anton, we might need your help with the paraview package. We need to figure out a way to build against system VTK libraries. This would help avoiding file conflicts and the vtk package would get a better test coverage.
