These technical things may all seem obvious to some on paper. The problem is, real humans have to perform in these scenes. How much fun do you think it will be to perform in scenes with “no hands” and having to stay perfectly still with “no fucking back” just so it matches up with some guy laying on his bed at home? If I’m a porn performer, I’m staying the hell away from those cold technical scenes with no passion, fun or intimacy. It sounds like the complete opposite of what porn should be.
I understand the intention of passthrough and the appeal of it looking like the girl is in your room on top of your body. In practice though, it will never truly be able to mimick that unless you make it so rigid and inactive that it becomes totally boring to watch.