Undo based on div block will be a time saver.

For example, I edit header, body, a button and the footer section over a span of 5 minutes.

I like the results of the body, button and footer edits. I realize I styled the header incorrectly and want to undo all my edits just to header section. 

A good solution:

Right click on Header block, display only header revision history with option to Under changes to Header block.