That feels like it requires the data model to be very different? The file format would essentially need to be a list of changes, with a "committed" flag.

Like, if someone changes some text in a paragraph, you can't just model that as "this paragraph now contains this new text". You have to model it as "this paragraph used to contain this text, but an uncommitted change changed it to this other text". User deletes an image? You have to still store the image and all the references to it, but with an uncommitted change to delete the image and remove the references to it.

And maybe that's a good thing, maybe a git-like system where the history of every change is tracked is what you want. But it certainly doesn't feel like it'd be appropriate for every application and file format.