Not long ago I read some article here on HN that the world is still waiting for a git equivalent for documents. This seems like a good start.

Now we need a native diff viewer for structured files, where the changes are presented with attribution either side by side, or alongside (like gitk, or like gitlab diff viewer).

Then we need an editor that supports doing the gitty stuff natively, so that the non-technical writer doesn't have to worry about creating repos and committing the changes from the command line.