Oh, I forgot to mention : I totally agree that the construction example you provided is, indeed, the most clean and accurate way to ultimately produce that form in proper NURBS - no doubt about that :)

I think what I am trying to get at is that the video I posted is more about "refining the idea" (like, holding the object in one's hand to observe it from all angles, and making minute adjustments accordingly to balance it based on a rough idea sketch) rather than building it accuratley ; I consider these two stages of the design process to be quite separate (yet informing each other). As you say, these "edge curves' would not be very loftable or trimmable. They would however work okay using the Network command - and even tho it would likely produce pinching and continuity problems, this is often good enough for my needs :D

Unfortunately and after years of searching I haven't found a great versatile (and fast !) environment to fit such needs ... IHeartSketch came close but unfortunately never got released and doesn't have any surfacing tools anyways ; Sketchup came close too but is quite stagnant ... and even sculpting programs like Zbrush or Mudbox just feel too heavy handed for the job. I also found an experimental university research focusing on modeling 3D forms from line drawings only but unfortunately it doesn't run on modern computers ...

I still have to investigate MOI further as there might be some tricks that I am not aware of that might already be doing what I want :D Looking forward to that!