I should explain...
If you "window" select all the curves in MoI, and hit LOFT; you immediately get Andrei's form. When I did that in Rhino, using "Loose" setting, it did not work. If I chose the curves in a particular order, then it works.
Just a bit faster and easier in MoI. Sorry for the confusion! :-)
Ron

EDIT: Okay, now I confused myself. When I quickly tried it the other day, the resulting isocurves were all twisted. Tried again now (as described above), and it worked fine. Perhaps I missed one of the curves before?
Anyway, still a creative use of LOFT, Andrei. I'll go back to lurking now! :-)