I actually used a copy camera that size at National Geographic. It was a Lanston Monotype which filled an entire room on the 2nd floor of the NGS building on 17th street in DC where the photo labs were located at the time. I was suspended from the ceiling on huge springs to isolated it from vibration. The film back was 30" x 40" and copy board about 6 x 8 feet, illuminated with banks of pulsed-xenon lamps.
To make the largest size NGS wall maps we would put a halftone plates from a smaller size — like those inserted into the magazine — and attach it by static electricity to a sheet of plate glass where the film would normally go, then using a carbon arc lamp with a motorized dodging paddle as a light source we turned the camera into a giant enlarger exposing the litho film placed on the copyboard in the safe-lit gallery section. The Schneider lens wasn't quite as large in diameter as the one shown in the link, but it had a focal length of about 42" and stopped down to f/256 if memory serves.
My dream camera would be a Canon 1.6 crop body with an EVF I could use my EF and EF-S lenses on without worrying about sync limit. I got spoiled shooting with flash with my EVF equipped Minolta D7Hi with its 28-200mm equivalent lens... http://super.nova.org/TP/DPS-9000.jpg
...but it is only 5MP and has the IQ and DOF limitations of any small sensor camera.
FF digital square format (i.e. 36x36) rangefinder with convertible 100% optical viewfinder.
Hey, you did say "dream" ... it just needs to use a split mirror (perfect with split prism or gridlines screen) that "pocket door" slides apart to reveal the sensor. MLA for rangefinder use, mirror together for critical TTL viewing.
By using the sliding split mirror, you negate the longer registration distance needed for the mirror to 'flip' up out of the way. Thus, you could use a registration distance like the M series, and would be able to mount everything from M to FD/FL to EF to F to M645, etc. via adapters. No more need to rotate orientation for portrait/landscape, etc.
Leica ... are you listening.
I'll trade you design rights for production models.
Square medium format EVIL with the resolution and dynamic range of the Phase One IQ180 with built in vibration reduction, sensor cleaning and swing/tilt and weather sealed. Hey, can dream can't I?
