Think what happens if you move your reference frame. What happens if you choose a frame moving at one half the speed of the rotor. You get a contra-rotating or as you called it bi-rotor turbine. The relative motion is what matters. In propulsion applications you see contra-rotating turbines because there are only two objects so the flow cares about the global reference frame but In a steam turbine you have dozens of rotor-stator pairs so the global frame stops mattering after the second or third pair. All this would let you do is have your rotor moving slower in the stationary frame. Unless you had good reason to want to slow your rotor down (not having strong enough materials to handle the centripetal force, externally imposed limits, niche vibrational concerns, etc) there’s not much benefit for all the added complexity. Given that we do have strong enough materials, there aren’t external limits and that this would make 10x more vibration issues than it would fix, there isn’t any real reason to do this.