Sorry to slightly diverge from the hip/shoulder discussion but...

Recently I've been put in a role where I had to help some fellow practitioners in their training, which is making me think hard about what I say or do in front of them. I've found that explaining movement (displacement) from the perspective of either front foot or back foot, could imply -- even if it's not meant that way -- that the "other" foot has a diminished or independent role. I prefer the approach where for example if I want to step forward or backwards, both feet/leg/kua are doing something; more specifically, they are doing the same thing but in opposite directions, which combined with whole body connection allows one to "move from the center". Dan has shared some drills that are amazingly good at helping stabilize hips and move from center. This was a game changer for me, and it's great to see some of my fellow practitioners who've struggled for years starting to fix things in a matter of minutes when they follow this model.