The old weight shift/edge and pressure snow plow turn is looked at as a dead end maneuver by many using elements that have to be untaught later. I have been wondering if the extension to initiate the new arc is something of the same thing. Like pushing the tails the 'up' move is firmly ingrained in most skiers. It is their release mechanisim, extend to disconect from the snow. Now I'm not saying that being able to un-weight the skis through extension is in any way wrong, in fact its a move that every skier should have. But for many it is the only move they have. Further, in many high level lessons rather than introduce alternative release moves the focus is in redirecting the extension as in 'don't extend up extend forward' still the extension to release the skis.
More later I hope, have to go skiing.
uke
This is one of those issues for me that has me miffed. I learned old school to start (this was part of it) and yes did it wrong at the beginning. It was a stepping stone into step turns, ultimately into parallel and later into carved turns (though these sort of occurred in the same short time frame). During this learning progression I learned to snow plow correctly. (These skills made the transition from straight to shaped easy, adjust the timing and balance points slightly and all of the learned skills applied.)
I find that skiers that have started on shaped skis lack this skill as they become better and as a result have difficulties mastering other skills as a result and have the same problem in reaching the advance status as we did on straight skis as they have not yet master the need intermediate skills (our lack of skills were slightly different, yet the problem is the same "lack of skill set issue").
So in saying Snow Plow is a dead end is very wrong, it is a skill set to be learned. Now if you say, with current equipment it may not be the best skill to learn at the start as it may hinder progress is something different all together. Or how it is taught may be wrong , is again correct. Schools of thought and instruction, sometimes are very slow in changing methodology even though equipment and methodology can advance quickly, hence some of the issues you see.
No offence meant towards very good instructors (bud, kneale and josh just to mention a few) as they do get it, adapt and teach what's required at each level. The reason they can do this is they understand the importance of a skill and when it is needed to take the next step. (Cheers instructors).
To be good you gotta learn it all!