I mean, I agree with all the acoustic principles you referred to but if we go strictly by those principles then technically the walls of my control room would also not be 'visible' by those lowest, most troublesome frequencies either.
Actually no, because the MSM wall works on an entirely different principle. It is a tuned system. Technically it is a bandpass filter that is tuned to the resonant frequency of the wall system. At the resonant frequency it is not only transparent to sound, but actually boosts sound through the wall. At frequencies above and below resonance, it blocks sound progressively better. Since the resonant frequency of your wall is designed to be as low as possible, and hopefully outside of the range of human hearing, it blocks all of the frequencies that are of concern to us humans. The walls of your studio will only be visible to the low frequencies if you build them wrong! For example, if you don't put enough mass into the walls, or have an air gap that is too small, or don't put enough fiberglass inside the cavity, then the resonant frequency will, indeed, be high enough that your wall will pass sound at frequencies where you don't want it to.
But that isn't related at all to the issue of sound bending around objects whose dimensions are smaller than the wavelength. That's an entirely different thing. In any event, since your studio is supposed to be sealed airtight, waves are not able to "bend around" the walls, since they are prevented from doing so by the walls themselves. The walls. floor and ceiling define the acoustic boundaries of the room. So in order for your cloud to be able to change the room modes, you would have to build it from wall to wall, and seal it airtight to the walls. But then it would be a ceiling, and would no longer be a cloud!!
I'm not so sure a cloud panel wouldn't have any impact on room nodes though.
If you build the cloud large enough and massive enough then it might, indeed, add new modes to the room. But it will not affect existing modes, since they are defined by the room boundaries, not by objects within it.
So if my cloud is really just comprised of mineral wool and breathable fabric than it will certainly have very minimal impact but if I make it with walls of some reasonable amount of mass - more like a bass trap panel.....
Then it would be a bass trap AND a ceiling cloud!
But it still would not have any effect on your room ratio, nor on the modes that are defined by the room boundaries, except perhaps to add a few more modes of its own. In order to change your room ratio, you have to change your room dimensions, and that means moving one of the bounding surfaces of the room.
Actually, if I only move that wall to the right just a little it would actually make the room more square.
You mean that right now it is wider than it is long? That means that you are firing your speakers along the shorter axis of the room, instead of the longer axis? If that's the case, then maybe you should rotate the room 90°, so that you can get the speakers firing down the long axis again.
- Stuart -
Especially since I'll have to be careful not to touch the caulking. 
The driveway is still caked with mud from all the work.....gotta get that cleaned up.