Stories:
As a quiz taker I want the ability to undo mistakes I make on a question while in a quiz, especially with questions that take a long time to answer.
As a course administrator I want to be able to view a more accurate history of the progression of a candidates response to provide information for decision making if an issue arises.
Optional: As a authorized person I want the ability to view and if necessary revert a question response to an earlier state after a quiz is completed

Proposal:
Modify auto-save functionality so that at configurable intervals instead of creating an auto-save it creates a standard save with the option of turning it off.
Add a button with a modal dialog that will provide the user with a list of previous saves that they can choose to revert to.

Considerations:
This change will result in more data being written to and read from the database when saving and loading question attempts.
It will require changes across many core parts of the question and quiz engine, this will probably require changes to the mobile app as well to maintain compatibility.