I have an idea for you.....
After reading the very long thread on "Judging the Flare" I was only thinking about this a few nights ago. Would it be tricky to design some system that involved a small distance sensing device that automatically came to life at 20 feet. This could be linked to a simple panel mounted display to show height above the runway.
I am not saying it should actually be used whilst landing but it would be a useful gadget for instructors to demonstrate height above the runway and to allow students to visualise from the cockpit exactly what height they are at.
OR.....
What about a BUZZER that goes off through the intercom when the fuel tanks need switching over?
OR.....
Some kind of sensor that can be installed into all new GA aircraft that records the "hardest" landing through the oleos. This tamper-proof system would make the next owner feel a lot happier if he knew what kind of stress his pride and joy might have been put through in days gone by.