It would be feasible to build a sensor that has binary pixels either black or white. If there was enough of those pixels the sensor would form a good image. As far as I know such sensor designs have been proposed.
Such sensors exist: they are called "film", where each sensel is a cluster of silver halide crystals that is either "exposed" or "not exposed" as far as the subsequent processing is concerned. All shades of gray seen in a traditional monochrome negative are dithering of a mixture of pure black at exposed "sensels" and pure white elsewhere. By any practically relevant definition, the resulting dynamic range is vastly greater than any "per sensel" value, and cannot determined at all from per sensel measurements. Dithering and blurring of the signal from multiple sensels each covering an angular part of the viewed image too small for the viewer's eye to resolve must be taken into acccount.
By the way, thanks for your effort on this.
Also, the Kodak/Truesense 50MP CCD has read noise of 12.5 e-, about the best for any of that brand of sensors, so your value is reasonable for CCDs as used in DMF. One source of such data ishttp://www.truesenseimaging.com/products/full-frame-ccd
and the product summaries linked to in there.
P. S. TeledyneDalsa just released details of a 60MP sensor which is presumably the same as or similar to the one that was originally exclusive to Phase One, only now offered openly to all customers:http://www.teledynedalsa.com/public/sensors/datasheets/FTF9168C_datasheet_20120306.pdf
This reports signal and noise specs in a different way, but you can convert back from well capacity (50,000e-) and DR (73 dB) to SNR in electrons, and I get just over 11e-.