The more I think about it, the more I'd like to see the 6D series become the niche low light full frame, like the A7S, etc.
No AA filter (or option to turn on/off).
Drop resolution to 13~15MP for larger pixels to improve ISO performance.
Scale ISO to compete at least a little bit with the A7S, etc.
Increase -EV for AF in center point (go beyond -3 EV).
Increase dynamic range a bit more (which should happen with the larger pixels).
Canon's 5D4 should compete with the similar full feature Nikon.
Canon's 6D series at least to me should branch away from the 5D series more and focus more on being the best low light full frame capable sensor for 4k video and ultra ISO (again, like the A7S).
Interesting ideas. A thread just popped up in a another area here talking about how photos from the 5Dc just have a great and unique look to them that not even the newer Canon cameras have. Its because of the larger pixels. I still love the way the shots I took from my 5Dc look as well and I can easily pick them out from shots Ive done with other cameras just from the thumbnails. I would be thrilled if it were 18-20mp but larger pixels and the images looked like a newer, better version of the 5Dc. Let the 5Dx (IV) play the megapixel game. I just got done shooting with a 5Ds I rented for a week, comparing it with my 6D. There is pretty much zero difference even at 100% and straight off the camera, much less once its been resized. Ive realized more megapixels is meaningless for what I do, I would value larger pixels a lot more.