I don't know how many others out there would like to be able to make water soluble supports, but I sure do. The problem is that PVA is water soluble but is unreliable to print with. I have a solution if Simplify would do their part. the PVA prints ok for short runs, but it is unreliable for a large support. If it was possible to set a second extruder to do just the dense support layers, where the support attaches to the part, then the pva would only have to print a few layers, and the rest of the support could be PLA. Then the support columns would just fall away when the part is placed in a water bath. This would solve a big problem for supports of hollow parts with inaccessible areas.
This would be really convenient. Currently the only way to do it would be through the use of multiple processes, which is only practical if all of your dense support is around the same Z height.
This feature request is already implemented in slic3r. Slic3r allows you to select a different material for the interface layer between the support material and the model. S3D needs this.