Interestingly enough, my level 3 prep group at Pro Jam also covered this topic. What we got was that there were 3 possible christy moves we COULD be tested on:
modern stem christy,
traditional stem christy.
The primary difference being tested for among these turns was movement of CM. In a wedge christy, the CM moves over the downhill ski to initiate the turn. In a modern stem christy, the CM stays centered. In the traditional stem christy the CM moves slightly uphill. We were told that the modern christy was a highly probable exam task.
Strictly from the viewpoint of demonstrating ability to control movement of CM, I'll (cough) buy this as a "valid" exam task. My group did not get an explanation of the validity/usefulness of the modern stem christy. I read between the lines on that to see it as a stepping stone uncovered by a low tide (i.e. it's there only because it's possible and may be useful in rare situations).
It was explained to us that exam tasks are simply brutally effective means of observing fundamental skills that may or may not also be effective as teaching exercises. My fearless leader also explained that when Killington has enough snow, that there is enough mountain that it is possible (but not 100% likely) to simply ski and by so doing demonstrate the required skills without performing any artifical tasks.
One other theme we got during the week was "options" as an element in high level skiing. This goes directly against the old criticism that PSIA promotes 1 way to ski. During our week we explored options such as retraction turns (collapsing both legs through the upper third of the turn instead of extending the outside leg) as a tool to add to our toolkit and be able to use should conditions (e.g. bumps) warrant. I also got the "options" theme from Michael Rogan at ESA. I smell a trend here. The non-wedge christies are simply tasks that (church lady like) conviently fit the trend.