Can an option be added to unlock a file in such a way that the next time it gets committed, it is automatically re-locked? Or to just have this done for all unlocked files?

It's a common use case to just do one edit / re-generation of a locked file. If you forget to lock it (or a script that was supposed to lock it after modification fails in the middle), you end up with a permanently unlocked file, which can cause performance issues downstream, and also look odd when missing, lead to multiple copies when present (or risk annex.thin issues), and leave the file open to inadvertent/unintended modification. Also, locking the file manually litters the git log with commits that don't really change repo contents.