How about just before you save an HTML module - you can insert comments for that change? In Community there is Preview and Version History. How about adding a field to add comments?
After correcting an intern's published change, I felt compelled to comment my fix because in Visual Studio when you check in a file you're given an option to comment on what was done. A savvy person could insert HTML comments however this would give non developers a way to record a more detailed history of the content.
What do you all think?!