Recently I found this article this article about the concept of directly sit on a pile of intermodal containers and lock them in place. Whether it is plausible to open such a huge opening ventral of such monstority, I found the idea of using intermodals as air freights attractive, as it eliminates the hurdle of taking the items two and fro between two incompatable systems.
Also similar but more radically engineered are the spanloader concepts, where the intermodal containers are just tucked into the wide, rectangular fuselages, or even into chords of giant flying wings themselves. Please refer to this thread (in which many of links require Wayback Machine to access and takes time to load alrge pdfs) to see their applications including even fitting ICBMs inside.
There are even far smaller concepts of ground effect freighter which is just one container-sized.
Then I am curious: why the current jumbo freighters, instead of unsightily truncated ULD, do not directly load intermodal containers onto their cargo decks?
P.S. Size and shape of fuselage should not be the problem, as such odd shapes were meant for thinner cabins like this answer, while not a problem for new-gen wide bodies like this, not to mention jets modified to carry oversized cargo.