I don't think holding breath will be in the game since it isn't realistic.
By which I don't mean that you can't hold your breath in real life - I mean in real life holding your breath does not stop your body from making slight movements which affect your aiming. In RO you simply rest your weapon on a wall, or on the ground if you are prone to stop it from swaying, which is realistic.
Less realistic games use holding breath just as a mechanic to balance out sniper weapons forcing players to stop moving in order to shoot accurately just because they don't have any kind of system where you can steady your weapon by bracing it against the environment.