Limits to ISO

I came across an interesting post on the limits to ISO sensitivity in digital sensors (linked from the online photographer). The assumptions are a sensor with 100% quantum efficiency that is purely limited by photon shot noise (not a bad assumption) and a full-frame sensor with 12 MP resolution. Basically to get similar noise characteristics as a D3s at ISO 6400, it would have ISO 96,000. That's an astonishing conclusion and would be a really fun camera to play with. Read the whole post for the fairly straightforward calculations that went into it. Current sensors are nowhere near 100% quantum efficiency however, in large part due to the Bayer array layout which throws away a lot of light as well as the high reflectivity of the sensor surface. Both can in principle be solved and there are already concepts out there that do so.