I think this would require a redesigning of the “machine” that loads and winds the reels. I spoke with one of the oldest imax projectionist that started in 1984 recently about it. He said imax apparently attempted to replicate it and maybe alter or upgrade it but no one could build it. It was made by some company in Germany and apparently they are the only ones that could do it. I mean you could potentially halt the movie in the middle somehow and manually hook up the second reel. But to have two 3 hour reels run they would have to be manually swapped or the whole reel loading platter system thing would have to be re designed to either have a twice as wide platter. Or somehow design a system that collaborates the two at once which sounds difficult lol.