Wanted Features for 4+ Axis CAM - Discussion

I'm going to work on writing a new open 4+ axis CAM for my oddball applications, e.g. CNC airbrush, 5-axis inkjet, hybrid 3D printers etc. I'm considering it to be an addition to FreeCAD but I'm not locked into anything yet. What features would you like to see for milling and turning?

Since FreeCAD was mentioned...no doubt your input would be welcomed.
It currently will map a tool path to a cylinder. Axial + Z + Rotation.
It will surface or pocket facets, like a hexagon. X + Y + Z + Index. Last I tried this was a bit buggy.
I'm not sure if it's capable of something like a herringbone gear but probably not. Any type of gear tooth profiles may be beyond it's current abilities.