Hmmm...here's Benni Raich. At shots 1,2,3,4 he sure looks forward on his outside ski looking at the angle of his ankle and the bend of the ski on the snow. 5,6,7 he's back on his heels. Rounding the next gate the outside ankle is bent and the ski is curved in the snow; looks forward to me.
Nikki Hosp...forward in shot 1, back in shot 3, forward in shot 5.
A contributor...neutral in shot 3, forward in shot 7 according to the ankle angle.
Some skiers may have the natural athleticism to know the feel of their skis when they are skiing just right and balance their body to get that feel. That includes bringing the CoM where it needs to be for the ski's best performance. They don't need to consciously re-center or pull the feet back, or whatever they do, unless they're thrown out of position by a bump, etc.
Some of us need to be able to get the skis loaded properly by making conscious movements. I need to pull both feet back at the turn transition point (the release) when I'm cresting over a bump or on a steep pitch. When I'm just cruisin' I'm able to drift my hips forward to get the fore/aft balance I need--gravity is pulling my body downhill while friction is holding the skis back somewhat.
Fore & aft balance or inside/outside balance? Both. The body is described in 3 planes. Frontal Plane - Also known as the coronal plane, divides the body from front to back. Frontal plane motion would include leaning from left to right. Sagittal Plane - Divides the body from left to right. Sagittal plane motion would include bending forward and leaning back. Transverse Plane - Divides the body from top to bottom. Transverse plane motion would include rotating the head or torso. (and if I mixed up any of these, pls straighten them out.)
The "CoM inside the skis" folks are talking about frontal motion. Let's talk about sagittal motion. As the pic of the guy in the orange jacket above clearly shows, we move in all three planes when we're skiing.
About ankle flexion...I feel that ankle flexion inside a ski boot is not an action. It is a result of leveraging the ski by moving the CoM forward (or the feet back, same thing, different point of view). If I had a ski boot that was flexy enough that I could bend the boot just using my ankle dorsiflexion or plantarflexion, the boot would collapse when I need to recenter after being thrown out of position or when I need to work the ski tip into the snow for tighter turns.
About extension turns and retraction turns...most of the racers free skiing in that video were making retraction turns. Don't focus on the body. Look at the angle of the outside knee and hip when they end a turn. If the knee and hip angle increase, they're retracting that outside leg. If the knee and hip angle straighten when they end the turn, they're making extension turns. Of course, when those guys are free skiing, their movements are so subtle that it takes a close look to figure out what they're actually doing.