There are legit reasons why relying on restoring to an archive to fix a mistake is a bad idea - agreed - and this is particularly true in a centralized catalog where you are not just affecting your site, but all sites. However, not everyone is part of a centralized catalog (the minority are, actually) and our users have been relying on archives as a restore option for many years. That said....
Bill wants everyone to stop using archives in this way - now.
"Archive for "undo" BAD PRACTICE, STOP IT" - his words.
In addition to simply noting that we removed this option, we need to say something to start encouraging users to stop looking at archives as their goto for undoing something such as a bad import. This won't be easy as users have 20+ years of being trained TO use their archives in this way and we have no alternative for them at this time (like an rollback or preflight). We can only state what we have done, and why, and encourage them to perform potentially dangerous operations during periods of low usage, to be more careful up front, and to review for errors immediately following the operation. Basically, don't screw up!
They can of course utilize the daily archives for disasters and they can always make manual archives using the options in /admin or the utility, and it may be worth noting this. However, the idea is to start steering users away from this thinking and whatever statement we start here in the release notes will help in creating future training articles, etc.