It would be nice to see to see the version of a file in the undo history.
When I am working on the same file for a longer period (with multiple saves), that would give me some more information on what happened when.
The most important use-case is when opening a file just for viewing. It is marked as changed as soon as the view changes.
Having that indicator in the undo-history would help me see if I can just close it without saving.