I think this is great advice for the advanced skier. I like your imagery of the feet moving one way while the body moves another. These are the kind of images that allow a learner to break down complex tasks and to focus on the components.
I was similarly inspired by watching boarders carve beautiful arcs to experiment with the relationship of the body to the skis in order to move further to the inside and further down the hill very early in the turn. In my case I was trying to move the control phase or active carving phase way up to the top of the arc. Back when I was on "straight" slalom skis this required an especially pronounced forcible leg extension against the skis which were essentially uphill of the body at this point in order to bend and shape the skis early. The effect of this was to allow the skis to accelerate through the remainder of the turn as well as allow the body to take the kind of "shortcut" you describe to arrive in the right place at the right time. That was awhile ago. I haven't been teaching or skiing very actively in recent years but your description effectively brings up my recollection.