Those were just my observations, I stand corrected on the Helix design. I am not an Eaton engineer. But it could also have to do with the strength of the rotor to lessen the chance of the rotors colliding with each other. As you can see the from the two older models that you showed the opening is not rectangular its simply wide open for air to move in any direction, so what I was trying to say is that the opening variances are not extremely important.
You are more then welcome to add things to the set up, but as it stands there is not enough interest for its current form, where cost is the main problem with custom parts for the SC.