A lot of the really old cartoons would use a background art image and would pan over it with the characters dong stuff to create a sense of motion. Sometimes the characters would move over a still background image but the 'camera's would zoom in.
Something that could extract the full size background image to apply it to the frames to enlarge the aspect ratio could go a long way toward revitalizing a lot of older cartoons. Especially fit could fill in any gaps using the opensource equivilent of Content Aware Fill (is there an FOSS equal?)
I've been trying to get my kids into Space Ghost Coast to Coast, Home Movies, Sealab 2021, the Simpsons, etc. If the video is wide screen they try it and enjoy it. If it's 4:3 they barely give it a chance because it's "too old"