HEADLINE: Allow rollback/snapshot of any change of system settings or package installs/purges
DESCRIPTION: It would be great if Ubuntu had an undo mechanism for any operation that changes the system settings, or the installed packages. Also, being able to snapshot system directories like /etc, /usr and /var would be great. Perhaps this can be implemented by running Ubuntu on top of a snapshotting filesystem like Btrfs. Of course, in that case, any system tools should be able to deal properly with background changes of the filesystem.