>>8287720It's side-to-side motion so they can stand flat-footed when their feet are spread wide. The easiest ways to do this are either by using a balljoint at the ankle, or inserting the ankle peg into the foot diagonally so the foot can rotate around it.
I agree that swappable feet would probably easily be lost sadly. I just want sneakers and flats on some of my dolls and that's pretty rare to find.
