I believe the point is something that one needn't use hand signals for. At least the last two links you provided (quoted) are things that augment and illuminate when using standard hand signals. This would be more something akin to a trigger shifter that would trigger right or left when depressed so that you can signal without getting out of a rain cape or moving your hands from the handlebar. It's doable, makes me wonder if it's a project I should take up.