Interestingly I would imagine pulling the non-CG part out of the frame would be possible as they have the ability to generate the exact image without the real-world aspects. Basically a virtual green-screen. Combine that with a stereo camera and the fact that the source CG is actually 3D and you could get very convincing 3D movies I'd think. Yeah, that simplified a lot, but I'd say it's possible. And they still get the benefits of the lighting aspects as well as the immersion for the actors.