One thing to keep in mind is that features essentially come free. The expensive thing is sensor surface area. Megapixels are free, square inches are expensive. Designing a 20-40 MP sensor at 6x7 would be much more expensive than just upscaling an existing sensor. A sensor based on the one used in the Sony A7s would fill the bill for you, that would come in at around 50 MP.
Keep in mind that such a sensor would really need an OLP-filter. The larger the pixels the more artefacts will they produce.
Sensor costs scale much higher than sensor area. Doubling sensor area may raise cost 4-8 times (I guess), and producing in small series is more expensive than producing in large series.
Another expensive development is the signal processing chip, Bionz, Expeed, Digic and it's programming. Deactivating the motion stuff is in all probability just changing a byte from true to false, but it may or may not reduce licensing costs.
Well, it seems that Sony can make large sensors at a reasonable cost, it may just happen that your dream comes true. But, in all honesty, I wouldn't bet on it.
Alright, I'm just a photographer, I'm not a pixel peeper or techie so don't jump down my throat for my simple minded question.
If Canon/Nikon can make low light cameras and sensors (or be it Sony's), why can they (any manufacturer) not make a medium format version that is a full frame sensor?
This is what I'm thinking; a low light CMOS, 6x7 sensor that is around 20-40mp for under $20k, live view would be nice but it doesn't have to do video.
My logic is that if Canon/Nikon can build a body with all the extra goodies in it (mount, titanium body, extra electronics etc etc), for under $5k why can they not simply cut a larger sensor out of the original wafer and throw it in a digital back for $20k?
Why are we locked into this 36x48 format or even 40x54?
be gentle please