Since you're looking for a new feature to add to a mod or concept, a "Principal's Pet" system would be a fun way to expand on the game's social mechanics.
: Maintaining high grades and completing "Good Deed" errands (like returning lost items or helping teachers) fills a "Pet Meter".
: Allows you to roam the hallways during class time without being chased by Prefects, as long as your meter is high enough.
: When your meter is high, you can "report" other students' misbehavior to Prefects or Teachers, causing them to get busted instead of you. You also get a "Warning" instead of being immediately sent to detention for minor infractions.
: Increases the speed at which you gain "Good Deed" points.