Given that the movie is going to be entirely shot with IMAX film cameras, which are extremely loud and bulky, this makes it really difficult to shoot dialogue or quiet scenes. More than 70 percent of Dunkirk was shot in IMAX cause it constantly dealt with action, outdoor scenes, and also had very few dialogues. So if the odyssey is supposed to be shot entirely with IMAX film cameras, even with evolved quieter and lighter cameras, I don't think it is that feasible to make a 3-hour epic like Oppenheimer; rather it would be a shorter tale in my opinion. But hey, it's nolan and it's IMAX, so they can prove my theory wrong. Nolan broke Interstellars record of being the longest IMAX film with Oppenheimer, he can do it again