The C11.17 tries to address these problems. It allows pictures to be made on multiple formats within the same image circle, and produces a larger aggregate format, 11x17, which some may find useful.
That image size is very close to a golden rectangle, if that sort of thing matters- and although it was never, as far as I can tell, a standard film size, it is a standard paper size. Film would have to be cut down from something larger, although it might also be possible to make a special order through Ilford's annual ULF run. 10x12 is another option, and sizes down to 8x10 seem quite feasible, particularly for colour.
Film is loaded in re-usable packets, which are slimmer than traditional holders, and lighter. Using composite materials, the target weight for a production holder is around 400g, although it might be possible to get them lighter than this, as long as stiffness and flatness is not compromised.
All holders are the same size, no reducing backs are necessary. Vertical shooting is made possible by removing the back and bellows as a unit (the back is carried on carbon fiber Arca style dovetail rails) rotating it 90º, and reattaching it to the camera, an operation that takes a minute or two, for casual shooting. Detaching the lifting lid and replacing it so that it hinges from the top takes slightly longer, although it does make for more comfortable shooting.
A camera dedicated to a single format will be smaller, of course, although not by much, if that size is 11x14 with a removable back. There is no denying that most 7x17's will be quite a bit smaller again, although I expect that the C1117 will prove to be the smaller of any system that can shoot both formats.