Era PC's katana had a feature where the player could create a temporary orb that would "stun" players within its range, causing them to walk at a considerably reduced speed for a short amount of time, hence making them easier to hit. This allowed for skilled katana users to hold their own against gun users. Of course this feature would probably prompt a nerf in the katana's damage otherwise it may be too powerful (probably a reduction down to 7 damage or so). I would be in favor of such an addition as it would make the katana better contend with guns, even with the nerf in damage.
On iDevice though, simplicity is the name of the game and that additional feature means one additional button in the UI, so with the sheath you're looking at 3 buttons which I would think would clutter up the screen of anything non-iPad.