I think that since the costuming conceals the legs so much, it makes it difficult to do too much with them. You have the pantaloons, the ultra-full long skirts, all the fringe and drippage. There are some slow steps that use weight changes from one hip/leg to the other, and the twisting foot on the Egyptian, but the most I can recall is Carolena saying, of various spins, that it doesn't really matter what you're doing to get yourself around, since much of it isn't visible to the audience anyhow. Not really sure what would constitute "expressive legs".

Not really. They are a big part of the movement, of course, but not really emphasized for show. With the big skirts and layers covering them, there's really not much need for fancy legwork. :}

also, traditionally in me dance the knees are kept close together because "we are good girls" (at least according to my first teacher) and also for safety's sake. if the knees come apart, the tendency is to get "duck butt" and your lower back becomes compromised.

Did I read the costume for ATS is designed to showcase the strength of the torso and gracefullness of the back? And like Valizan said, almost all top teachers I've read said the legs are not attractive when they're powering a shimmy.

"if the knees come apart, the tendency is to get "duck butt" and your lower back becomes compromised. "

If I may interject, what should be keeping you from getting an unhealthy sway back while dancing is the engaging of the lower abs, lifting through the top of the head, and a slight bend in the knees.
I personally find it much easier to dance with my feet a little less than hip distance apart just to give me a comfortable, stable base to dance on.

Great question, Soleil! Legs definitely aren't featured in ATS as they are in BD forms that, e.g., show bare legs through slits in the skirt or pantaloons. But I feel that legs do play a subtle role of their own in ATS, even under our voluminous skirts, by creating shape and a sense of movement.. E.g., in traveling backward with the Walking Bodywave, you might see ATS dancers whoosh the traveling foot/leg out to the side and back (rather than straight back), giving a lovely leggy poof of the skirts and an extra sense of mysterious motion. Or again, in a Reverse Turn, pulling the right foot behind the left to prepare for the turn creates a lovely vase-like shape from the hip down. Another instance is something Carolena N. does: when moving from a more flat-to-the-front movement such as Taxeem into a more diagonal movement such as Bodywave, she steps the left foot back and rightward, rather than stepping the right foot front and leftward. A very subtle difference, but to me, it's magical.