I see so many saying that the 1dx is being replaced or that this will be the successor to the 5d3. What kool-aid are you guys drinking? Maybe in the rebel world we would see such a rapid move to push out a new product, but not with pro level gear, or near pro level (XXD line). Canon hasn't put out a replacement for the 60D yet, which is a line that gets updated every 1-2 years. So to think we'll see even a rumor for the 5d4 in 2013 is a dream idea - more likely we'll see the dev rumors in 2015, with a potential release in 2016. (Id say the idx will follow a similar pattern...
You are nuts if you think it makes sense for them to wait another three years to catch up on sensors.
Big MP --- I am pretty positive that a big mp body will be aimed at a niche audience - studio, landscape, architecture - where the 5d3 is aimed at weddings and event shooters and the 1dx is for wedding, events and sports (5d3 can do sports too, but the slower frame rate).
Landscape is niche? General landscape and scenics are some the major usages for DSLRs.
5D3 was aimed at all around, landscapes (although they got left behind for DR), weddings (again with the DR), sports where your job is not riding on having THE frame ALL the time, it's decent for wildlife (only the reach is a little low compared to current APS-C cams or a D800), etc.
I think nikon jumped the gun a little bit with big mp's by trying to make such a camera to act as an all around work machine.
If you are bit more biased towards wildlife or landscapes than run and gun PJ or weddings, maybe they didn't.
Just a shot in the dark here, but my guess is that we'll see 2 big MP bodies in 2014, a 1d style and a 5d style (not sure what they will name them). Both will probably get the 1dx AF system, digic 6, one will be in the 8k range and the other in the 3-4k range. Neither will have fast frame rates, guessing 2-4 frames per second (1d style will probably get the 4 fps, 5d style would get 2 fps). Emphasis would be on IQ not speed. This would enable canon to funnel this tech into the next round (yes, this would be the 1dx2 and the 5d4). it's a sensible plan - get the new sensor out into its niche market, then by 2016 we'll have digic 7 or 8, our PC's will be that much faster, memory card speeds will be faster and their capacity will be greater and their cost will go down, how about some usb 4 maybe?
Really so they will put out a TWO fps 34-40MP camera for $4000 in 2014 when Nikon has a D800 for $2500, 36MP and 4fps (5fps at APS-H and 6fps at APS-C and with grip) out in 2012? So a product that is two years later, almost a cycle later than the D800 will not go up 2fps to 6fps FF but will drop to 2fps??
(Imagine transfering over 2000 45 MP images via usb2, lol, you have lost productive workflow time before you can even begin the workflow at that rate!!!!)
You can get a half-speed USB 3.0 card for a PCI slot or a firewire PCI slot card if you don't want to upgrade motherboards yet.
One place is way ahead now, largely thanks to Magic Lantern, is video. Man the 5D3 video utterly blows to pieces anything you get out of Nikon.