well, would be cool if the tech in the game could develop, but you only really need 360 rotation as a defensive measure, usually against being attacked from below or above. With the current state of aircraft and weaponry in this game you dont actually have to worry about that too much. It would be a defense against biplane attacks, but only really from below, the top is blocked by the baloon(on most ships). so any biplane pilot worth his virtual salt would avoid that bottom turret that is specifically designed for defense against him/her. and attack from the top. then we are back to a pilot positioning the airship so the top guns can kill the biplanes.
so all in all a 360 turret would be cool but its a defensive thing, with the current way ships work, its not needed. and when biplanes are involved, its a defense that is not needed unless the AI is suicidal.