Thanks for chiming in. We thought that the VTK community would be excited about the possibility of executing filters on the GPU but from the discussion above it seems that not many people are interested. So, for now, we’ll probably keep prototyping in 3D Slicer. We plan to develop it further and connect it with GPU volume rendering at the next Slicer project week in Boston, if you can come we would be happy to work with you there (or at subsequent project weeks).
In the meantime, if you have some processing implemented in GLSL already, then we can help in getting it working as a filter quite easily.