Plasticity is one of the easiest and cheapest Nurbs modellers available. I would love to see live connection from Plasticity to ArchiCAD. This has already been successfully developed from Plasticity to Blender, and from what I can see, it is merely an OBJ export, with a settings dialog in Blender. I believe this is written in Python, so I Imagine something similar must be possible for ArchiCAD.
This would be perfect for producing sculptural forms in as a GDL object / morph.