Canon's largest CMOS sensor, light gathering in practice?

Re: http://www.dpreview.com/news/1008/10083101canonlargestsensor.asp

So the large sensor will be able to gather more light, that's great. But, the comparison with the DSLR has to account for the lens' f/number right? So, if I wanna capture an image in "one hundredth" the light of what I can with a f/1.2 lens on a 5D, one has to use an f/1.2 lens on the bigger sensor. I would imagine that such a lens is not feasible, so anyone knows what kind (specs) of lens would a camera with this sensor use?

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Andy

Someone mentioned Canon having a 1200mm f/5.6 lens in the other thread on this. Telephoto lenses can typically project a larger field of view than the camera can actually accept. The crop factor of this sensor relative to 35mm is calculated at 0.15x. So putting this 1200mm lens in front of that monster sensor, you can have the equivalent of a 180mm f/0.84 lens on "full frame" (which is not so full anymore compared to this )

But a big mirror telescope on an observatory would probably be a better match to this sensor...