This came up in https://community.kde.org/KDE_Linux/Calls#Misc/questions. Essentially, if you roll `/usr` back or forward, the system should do the same for the version of `/etc`, or else they get out of sync and could poison the rollback. This would also neatly address the case of a user who breaks their system by doing something inadvisable that gets recorded in `/etc` (e.g. masking systemd or similar shenanigans).