[jandinter]

It is challenging, very much so, but it can can be done. I built a prototype for Word files based on Git (can also use the GitHub API, so making it work with the Dropbox API should be doable). I implemented sort of a blame function as well: Jump to the previous version of a paragraph with just one click.

As OP said, it took a lot of effort to get the UI ok. Probably takes even more effort to create a great UI, but I guess Dropbox has some resources, right? Shameless plug: Landing page at https://julesdocs.com

If anyone is interested in pushing this forward, I'd love to hear from you (mail address on the landing page)!