Very good idea. Have several versions of the song data - excluding audio - in one file.
A thought about that: What happens if the audio data changes? E.g. by hitting the "Save and Optimize" function, or cutting & deleting parts of tracks? Would that create versioned copies of the audio material? Or would it get rid of all older versions and reduce the file to just the current one?
Probably the last, I guess.
Maybe it would make sense to have both approaches