I've had another idea!
A simple "cockpit-cam" for flying schools to monitor how their aircraft are looked after when hired out, for instructors to analyse their students performance after a first solo and for students to take a copy of their training nav. flights home to watch and improve etc.
It could have sound from the intercom that records all radio-work.
Not only that, but the quality of instructing might get even better if the hour-building instructors know they are being watched!!