Here is a couple visuals of me fooling around with it...

I thought as Blowlamp and just used a Vcarving program to generate some gcode, then I converted the gcode to dxf and brought it into MoI. I could do a simple loft on the outer profiles of the toolpath and get the vcarve surface...



The second one is my "fake" vcarve. It's fake because the proper calculations for a vbit or specific tool, to rise and fall in the shape aren't attainable with my eye.. I just made a shape that looked kindof "vcarvy"... It does show the surface trimming thing that I think Blowlamp is referring to, though... I've attached a 3dm of the second method with the surface and the curves I used....



The file I posted is a little different than the video. The file has just a center morphed curve, rotated by "end" down to a depth. The 2 meet up, and are lofted and trimmed the same as the video...