It's been a while since I had a wacky idea but I got one in the middle of the night.
Here it is: the upper arm should be twistable so that you can rotate a camera to put the diagonal of the frame vertical without using a lens ring.
The usual aspect ratios of images are 2:3; 3:4 and 9:16. A little trigonometry would give you the angle of the diagonal. A three stop system would be good enough to get the diagonal of the sensor nearly vertical.
I won't attempt to justify the need for this. Some people will already understand the need -- many won't.