A company like Canon is doing alot of R&D. The magic phrase for prototypes like the 120MP sensor is "proof of concept". You are testing certain aspects. The 120MP sensor has shown that you can do multiple line read outs at a time and produce stunning speeds, which is now famously featured in the 1DX. There you go, a 2010 prototype lead the way for 12 FPS. Another issue they observed with the sensor was, that you are getting diffraction blur at such a wide open aperture that it is currently (2010) not managable to deal with in a finished product.
There is not a shred of doubt that we will someday have 120MP FF or even MFT sensors. When Canon is launching their new 1Dsomething with 120MP you can be assured that it will feature an all newly developed sensor. They won't just take the 2010 prototype and mass produce it.
Another prototype they did is actually now boing used. The ~20cm by ~20cm CMOS is used to map space in an observatory located in Japan. Like most astronomy telescopes and imagers they are one of a kind. Produced to specific uses.
A camera featuring a 20cm by 20cm CMOS and a fixed 43mm (35mm equivalent) lens would be a truely awesome piece of photography gear I would crave for!
Imagine this scenario. You are out at night on the streets with a model. The moon is shining. You found a good spot for some nice fashion portraits. You take your camera out and start doing your "photographer thing", then you say to your assistant "hey dave, go kick out that street light over there, I don't want to use ND filters tonight".