There is a flip side to this - is vim encrypting this data it keeps forever? If I delete something I consider sensitive, I might unwittingly be recording that presumed-deleted piece of data to my user profile somewhere to be deleted never.
Vim's persist undo is disabled by default, perhaps for privacy reasons. edit: I see sebzim4500 got there first.
Stop looking for post-hoc justifications for behavior that is clearly wrong.
How could you possibly encrypt it in a way that holds water? Any attacker who cares enough to get your undo file can also get your undo keys, unless you want to wire a whole system of undo-now-requires-password-auth-with-MFA
Not really since the feature is opt in
That doesn't justify its deletion, it might justify warning the user, but unconditionally deleting data not owned by the app shared with other apps?