Seat backs on airliners are now stuffed full of electronics. This is increasingly to take the minds of passengers off the fact that they are squashed into tiny seats.
When a seat is also being repeatedly kicked by someone sitting behind, or forced into contact with your kneecaps by someone in front, electronics can come to your rescue.
Rather than having an episode of air rage, if seat backs each had an iPad-like device on board (as they do) then the integral movement sensors could detect repeated impacts and wirelessly communicate this to cabin crew.
This would allow miscreants to be dealt with officially before complaints and acrimony set in. Just the foreknowledge that they might be blacklisted could force people to behave better.