My thing that needs to be invented is a inexpensive kit to convert a cruiser bike to a trike. Something that would allow someone to go out and buy a used bike for peanuts and use the wheels to convert his old bike to a trike.
All it would be is an axle that would require one to do would be to move the rear wheel outside the frame and add a second one outside the frame on the opposite side.
I know the trikes they make are only a couple of hundred bucks but what the heck a moped isn't much more than a bike we make.