Is it really the discouragement which should be the issue, or is it moreso the encouragement of adopting an externally (aka lateral) rotated hip alignment too. Like encouraging sitting cross-legged is good, doing so stretches the muscles which internally rotate and adduct (I think transverse adduction more specifically) the hip muscles. Tightness in those muscles is likely the reason it's difficult to adopt this posture at first. Heck, we have this problem even as adults, how many of us can get out knees to the ground in a butterfly stretch?

I can see how this could be bad for the hips, it's a similar criticism to the hurdler's stretch in track and field. Even so, I don't think we should totally give up on it, just make sure people don't spend 100% of the time, because you can get the reverse problem where you have tight external rotator muscles. You could develope mobility problems later in life if you don't maintain the ability.

For example, on these A-Z tips right after the deadlifting videos there are a series of stretches for tight external rotators to retrain the ability to internally rotate the hip that we lose, perhaps because of our focus on negative avoidance of internal rotation rather than positive training of external rotation (which is incredibly important, this is correct, beyond mobility encouragement it helps with stuff like proper squatting posture, hip extensor recruitment, and if you want to do proper ballet turnout or side splits for martial arts without stretching improperly.).

These illustrations should begin roughly next to the 'I is for Integrity' section. There are 2 test pictures, 1 mobility video and 1 lying stretch illustration relevant to it. The actual section referring to it is 'Q' though not really needed (and I don't want the Stano shot annoying anyone)

Furthermore also the final picture on the right side of this article shows another example of an internal rotation stretch.

Sitting in W may be an unhealthy way to train internal hip rotation. It does look like it compresses the knees and I know personally I find it really painful. However, if a child is discouraged from sitting that way, I wonder if it might be beneficial to introduce some of these stretches as a means of making sure a reverse imbalance does not occur. When I tried them they were not painful like W sitting, I think because there is not weight on the knees so you begin rotation more from the hips just like we do with cross-legged sitting and butterfly stretch.