Interesting to see all the twists and turns of this (sorry about the pun). Si was careful to qualify the discussion as being about "short, dynamic, high energy turns". And he noted he generally skis on two skis - a contrast to those here who assert that lifting or extreme lightening of the inside foot is basic technique. In general, a solid two-footed skiing style delivers more stability and more margin for error recovery. And the last time I saw Si he was a substantially better skier than I was. And thoughtful. So I'm going to guess he is not likely to trade that stability off for nothing.
My quick thought - in primarily carved really high speed short turns you need two things. You need the ski(s) edged enough into the snow that they can hold the lateral forces generated. And you need to really flex the ski(s) to the extreme to generate a consistent short primarily carved turn. And that's an interesting combination. Especially when both have to happen fast.
While 12 meters is small in terms of sidecut radius, it is not exactly "small" in terms of really tight turns. Pace out a circle with a 40 foot radius. Now think about linking turns of that scale. Even "incomplete" ones. Now think of how flexed a ski needs to be to bang out a primarily carved really "short" turn with say maybe half (or less?) that radius. And how quickly it needs to be driven into that state.
Bottom line - my bet is that this is one of the few (maybe the only) circumstances where giving up the stability of two feet is compensated for by the combination of rapid edge engagement and dramatic flex appropriate to the conditions and intent. And of course the two are not exactly independent issues.(of course by today's jargon, I'm not qualified to walk or to talk in this forum )