When will you guys get it? With the EF registry distance of 44mm you can't have a mirror that will give you a short side much over 24mm. It has nothing to do with lens baffles or image circles. It is impossible to make a reflex camera with a 44mm lens registry distance anything over a 26mm square, even a non moving pellicle mirror can't do it. The only way you can realise a longer short side, and see through the lens, is to read off the sensor.From 24 X 36mm to 30X30mm, the "Shortside" onlyincreased by 6mm, ie. 3 mm on each end of the "short side". If you look inside the film slr or FF dslr. You can see that there are easily 3mm space between the edge of the view finder and the insde of the camera body. This space is "reserved for the morror movement. If we think outside of the box and put the mirror hinge at the bottom of the camera. It may be doable.
The mirror is on a 45 degree angle, so 6mm of sensor equates to 8.48mm of mirror ( 6*sqrt(2) ). There is only 44mm from the front face of the flange, to the film (sensor) plane. Being able to flip up a 43.27mm mirror in that space will be tight, to say the least. With careful body design, it may
To flip down, you would probably need even more room, because then you have to clear the shutter too.