As I understand it only certain bits are filmed for IMAX 3D and the rest conversions from 2D.
I’m not interested at all. 3D despite claims is not realistic and quite distracting. It’s confusing to the brain as you cannot focus where you want, you focus where it’s shot to focus. Although 2D is fixed focus also, it’s less stressful on the brain. I find the layered effect with 3D just weird, and anything close to the camera can make you go cross eyed. At the cinema they typically use polarised glasses, which while is a better system it also decreases the amount of light that gets to your eyes.
In all, it’s just a gimmick to boost ticket sales. It was the same in the 50s and the same every time they’ve tried it.