Really?
Apart from the obvious concerns of whether it's safe (from an EMC point of view) to be discharging a stun gun in an aircraft cabin, the other concern often forgotten is making damn sure that it can't be used against oneself. If airlines start tooling up like this in a major way then one might wonder what the pre-boarding security check is for. There's an obtainable stun gun provided free of charge (pardon the pun) on the plane.
Same goes with air marshals carrying their weapons on to aircraft. It's fine so long as no one actually knows who the marshal is, something that is increasingly difficult to conceal in this day of social media. Services like Facebook with their facial recognition are beginning to make it possible for anyone to identify anyone else, carelessly set account options permitting...