It would, at least, create a codec-neutral location and format for image metadata, with codec-neutral (and ideally extensible + vendor-namespaced) fields. EXIF is just a JPEG thing. There is a reason that TIFF is still to this day used in medical imaging — it allows embedding of standardized medical-namespace metadata fields.
Also, presuming the container format itself is extensible, it would also allow the PNG approach to ancillary data embedding ("allow optional chunks with vendor-specific meanings, for data that can be useful to clients, but which image processors can know it's safe to strip without understanding because 'is optional' is a syntactic part of the chunk name") to be used with arbitrary images — in a way where those chunks can even survive the image being transcoded! (If you're unaware, when you transcode a video file between video codecs using e.g. Handbrake, ancillary data like thumbnail and subtitle tracks will be ported as-is to the new file, as long as the new container format also supports those tracks.)
Also, speaking of subtitle tracks, here's something most people may have never considered: you know how video containers can embed "soft" subtitle tracks? Why shouldn't images embed "soft" subtitle tracks, in multiple languages? Why shouldn't you expect your OS screen-reader feature to be able to read you your accessibility-enabled comic books in your native language — and in the right order (an order that, for comic books, a simple OCR-driven text extraction could never figure out)?
(There are community image-curation services that allow images to be user-annotated with soft subtitles; but they do it by storing the subtitle data outside of the image file, in a database; sending the subtitle data separately as an XHR response after the image-display view loads; and then overlaying the soft-subtitle interaction-regions onto the image using client-side Javascript. Which makes sense in a world where users are able to freely edit the subtitles... but in a world where the subtitles are burned into the image at publication time by the author or publisher, it should be the browser [or other image viewer] doing this overlaying! Saving the image file should save the soft subtitles along with it! Just like when right-click-Save-ing a <video> element!)