My question is: if it is indeed 20MP, why the heck did they develop yet another FF sensor?
They're Canon. They did it because they can.
As long as they can increase the DR, 20MP is enough.
I agree with increasing the DR, but I'm skeptical as any other. Not saying it's impossible, because people did welcome the 5D series and knew what they were sacrificing performance wise, just so they could get the IQ. The 5D mark III is a beast with it's AF performance. A lower 5D with more DR is what we're all hoping for, judging from Canon's habits... Most likely not going to happen. As for the sensor, they do make their own sensor unlike Nikon who has to depend on Sony. Canon has repeatedly used the 7D sensor without releasing completely brand new sensors (aside from small tweaks) in the crop line, and perhaps in that time they developed a secret line of new sensors including what's rumored to be this 20mp one. Or... They just used that time to develop their new Cinema cameras, and we're still pretty much screwed for new bodies until they can recover. In the meantime while we all wait for that, I'm still enjoying shooting because of Canon's awesome lens lineup.
An increase in DR won't make any difference if it has fewer than 24MP.
It would need to have some kind of extraordinary DR, like 16 or 18 stops, maybe 20, for it to make up for the lack of megapixels in the eyes of the average DSLR shopper.
I thought with the 22MP 5D3 that Canon would do something special for video because of the 3:1 ratio for 1920x1080 but it has delivered nothing special, so we were all wrong about that.
All of this means that Canon's strategy for this evolution of sensors and cameras is wrong.