Doesn't this assume you don't know the focal plane? If you know what the viewer is focusing on, you can compensate. This means that without any holographic projection techniques, you could fully solve this problem by presenting each viewer with images customized to his detected focus. That might require an expensive headset today, which radically changes the economics of 3D movies, but it doesn't require a breakthrou…
Have a camera facing the eye that can tell what the person is focusing on. (High end video cameras already have this.)
Have an adaptive lense in the glasses to vary rapidly change the focal plane from where they eye things it is to the screen. You then build software that blurs the image outside of their focal plane. Granted there are limits on this aproach, but people get used to glasses that have a fixed shift in the focal plain fairly quickly so it should be possible.
Now I don't see how you could extrapilate that to a theater full of people, but you can build a system that works for 1 person.