A 120fps master will be useful for 3d at home where the technology relies on rapid alternation between left and right eyes, so the effective fps per eye will be 60.
Although, now that I think about it, it might be useful for theaters, too, since they're using two polarized source frames per projected frame. It depends if they're counting the combined, projected frame as one frame or as two source frames to reach their 120 fps claim. Actually, out of curiosity, I read up on how Real 3D does it, and they use alternating, polarized frames out of one projector, which would be 60fps per eye.
Although, now that I think about it, it might be useful for theaters, too, since they're using two polarized source frames per projected frame. It depends if they're counting the combined, projected frame as one frame or as two source frames to reach their 120 fps claim. Actually, out of curiosity, I read up on how Real 3D does it, and they use alternating, polarized frames out of one projector, which would be 60fps per eye.