"We all know that the person going forward has the right of way, and the person going backwards is the one that clears a path. If this is not known we are in big trouble and would be better off with a spine made of rubber."
In reality, both partners need complementary CBMP shapes to make space for the outside partner step. If you literally get out of the way, you'll waste all your energly slingshotting around each other.
Most dancers except for at a high level end up reversing their hips almost to the opposite of CBMP during the course of placing the outside partner step, so someone is going to be off balance, distroted in shape, or simply going to have to get out of the way.