I would suggest to provide the ability to enter an optional edit message when performing a rollback. You could use the edit message to further explain the intent of the rollback.
$ git revert is a good example.
For instance, yesterday I rolled back a closed question to a previous version in order to reinstate the "Possible Duplicate" message that was intentionally removed by an user (causing the question to become useless with no reference).
Because the user edited the question a few times, I wanted to explain the reason of the rollback and I was expecting to be able to enter a message.
Note. I searched for this rollbacks feature request, but I didn't find any result. I apologize in advance if it was already suggested in the past.