I think that there's a strong argument that the IQ140 is almost ideal
...and P45+ *is* ideal!
Some shift stats of landscape orientation:
70mm image circle (wide angle Rodenstock Digaron-S)
54x40: 2.3mm/5.8% rise/fall, 1.8mm/3.3% shift left/right
48x36: 7.5mm/21% rise/fall, 6mm/12.5% shift left/right
44x33: 10.7mm/32% rise/fall, 8.9/20% shift left/right
90mm image circle (wide angle Schneider Digitar, Rodenstock Digaron-W)
54x40: 16.0/40%, 13.3/25%
48x36: 20.0/55%, 17.2/36%
44x33: 22.7/68%, 19.8/45%
I think a suitable shift range concerning composition possibilities is that you can get horizon up to 1/3 of a portrait shot (which actually is the shift range used in for example the TS-E 24 and PC-E 24 for Canon and Nikon). More than that is overkill, less is a bit limiting I think.
With that target, the 48x36/49x37 crop with 90mm image circle is the best balance. The 70mm image circles is a bit limiting even for the 44x33 size, then I rather go for 54x40 at 90mm.
The widest at ~90mm is Schneider Digitar 28XL I suppose, which is ~20mm 135 equivalent for 48x36, ~18mm for 54x40 and ~22mm for 44x33. And we have the Digaron-S 23mm which yields ~17mm for 48x36, ~15mm for 54x40, and ~18mm for 44x33.
Concerning lens designs it seems to me that 90mm lens circle with 6um pixel resolving power target makes it feasible with the traditional simple lens designs large format is known for, while when you go for higher resolving power you get much more complicated designs.
I think it would be unfortunate if future digital back development will only hold very small pixels and high color cast issues, which would lead to that these designs are made obsolete and put out of production. Because if you only need ~40-~50 megapixels you can get a very well-balanced system with the traditional distortion-free lower cost lower weight and more robust designs.