In principal, a zones editor is dead-easy. Drawing the spheres and boxes is the least of the problem...
In reality though, S3D's way of working with files seperately (dat, zon, etc) in different windows, makes it a little tricky. If I want to give a live preview it requires that both files are opened simultaneously. But it must be easy enough to switch between both while maintaining 3D state (in DAT-window), and undo/redo support (in ZON-window). This is the hard part. So possibly I may drop this idea and make a seperate zone editor which is not integrated in the current UI/viewer.
I am still working out how to do this best. It will come, just not sure when yet.