Well, afa qinna, there's more than a few applications using the Yang form; but, they are inherent in cmas. There are people who will demonstrate a qinna application for Ward-off or and part of Grasp Bird's Tail; and there are people who don't.
The stuff about doing the form on both sides is interesting. Yeah, if you're going to teach people in a studio with mirrors, you can keep your back turned, and the students can mimic your movements while you watch. If you're somewhere with no mirrors, then facing the class while demonstrating is cool.
The first person I heard about doing a Yang-variant form on both sides was Lee Ying Arn. Here's the thing. Like Bao said, the sides are not the same. We didn't have a special "left-side" class. If we did the opporsite side, it was on our own time. In fact, imo, that was the idea. I.e., you had to teach yourself. It was just like teaching a beginner. In fact, how could you hope to demonstrate the opposite side to a beginner without being as good on the orthodox side?
That leads to a paradox. If someone can immediately do the opposite side form, the the orthodox side was enough. Otoh, if someone can't, then it may take a considerable time for the opposite side to approach the skill of the orthodox side. It's possible, but it's like learning to throw and catch with the other hand. Hey, don't get me wrong. I'm 1000% in favor of ambidexterity.
Anyway, should left-handed people learn and do their form opposite to a right-handed person?