Northlight Images breaks down a sensor patent from Canon that shows a way to subdivide high and low sensitivity pixels.
Echoing a Nikon patent from November last year (7th) Canon look at ways of subdividing pixels into high and low sensitivity sub pixels or even high/medium/low triplets
“Variations of this approach have been tried by numerous manufacturers, going back to Fuji nearly 10 years ago. Designing the pixels is one thing, making all the rest of the circuitry to process the information for every pixel has been slower to appear.”
I suspect we're going to see new sensor tech to improve sensitivity performance in the upcoming EOS-1D X Mark II and EOS 5D Mark IV. There is probably going to be a lot more sensor tech patents showing up over the new few months as the cameras get closer to launch.