I'm thinking of building a productivity tool in the legal space. The big inspiration I had a week ago is that I could use git or another version control system for features like git-diff and git-blame.

I'm now thinking about how most elegantly add markup features for things like highlighting text, adding labels, inline commenting, muti-media embeds, and text formatting both simple and complex. any suggestions? The naive thing to do is to include a <span> based markup format that complements what is already being done with font-size,color etc but im worried that it will become a mess. Both in terms of document size and git diff.

also, are there any examples of products that successfully leveraged version control systems to create large project management tools?