You have three options (well, four)
-
directly intervene with the user and indicate there will be consequences for future negative behavior (casting lots of inappropriate flags)
-
turn down “max flags per day” globally in your site settings
-
lock this user to TL0
-
reduce flag sensitivity in your review dashboard, so it takes a higher cumulative flag score for thresholds to be met
I suggest you try those out before jumping to “discourse must add a new feature because of {problem user}”.
That said I am not opposed to limiting flags per day for low flag reliablity users, it is a sensible direction.