Such events are not very common and I wouldn't consider this feature essential. You can already do this by manually editing the post, it's just a bit harder. When you want to rollback an approved edit, you can use the following work-around:
- Go to the Revisions history for that answer
- Find the Revision before the incorrect edit -- i.e. the most meaningful revision
- Click on the Edit link
- Type the reason for rollback in the Edit Summary field
- Save the edit
Example revision history:
![Screenshot][1]
See also: