Hmm... As I said, 3D cannot become retro, the way 3D is rendered is what becomes retro! I think there is a slight problem in the question formulated here, it got confusing. How do you deprecate 3D? With VR? If someone makes a VR kit, how will pictures in it be depicted? In 3D, of course.
True, but they aren't going to called it 3d. Some marketing wizard will think up some fancy new term to catch everyone's eye.
However, what about holograms? If the technology becomes available fir the right price, they won't call that 3d. It all really depends on is what's available 20 years or more down the road.