6d using rebranded 5dIII sensors?
Typically all digital sensors suffer from dead pixels, but with the way interpolation works you can easily map out the dead pixels. This is the case will all Canon cameras, if your camera has dead pixels you can even send it in to have them map them out so they don't show up.
Maybe the sensors in the 6d are actually 5dIII sensors that when manufactored had too many dead pixels to meet the full stated 22.3 MP, so they slightly modified them and put them in a different cheaper camera.
I think if you look at the camera that way it makes more sense, Canon is giving you virtually the same 5dIII sensor, but with as much stripped out as possible to cheapen the cost by the 1400 dollars.
I bet when this sensor gets tested it's a near identical performer to the 5dIII, same DR same noise, same bit depth, just slightly less resolution.