Hard to say what Canon is up to. I would definitely say that a high MP, high end EOS 1Dx (not to be confused with the 1DX) is in the lineup but the second body?
The 5D3 is still pretty much leading edge and the 6D is also pretty new so I can't imagine a "replacement" for either one anytime soon. (perhaps 2015) With the rumored 7D2 leading the APS-c lineup again I would venture a guess that a second FF body (IF one is released) would be a smaller version of the high end EOS 1Dx like the Nikon D800 or D800E.
Seems reasonable to me IF Canon follows Nikon's current offerings. Canon has been stagnant lately in terms of their camera offerings and sadly so has Nikon to a degree.
They offer so many camera bodies that are so similar to each other it really makes you wonder why?
Think about it. With the 60D with a 18MP sensor and shooting at 5.3fps and $600 cheaper than the 7D (not talking about sales) why would you buy the 7D? MOST people don't realize how certain features affect real world shooting, so price DOES play in in buying a first camera. Canon has so many cameras that are so similar it doesn't make sense.
I mean really? The SL1, T5i and the T3? THREE entry level cameras? Why? The T5i is a great camera, ONE entry level camera is fine, really.
Almost seems like Canon cares more about video shooting lately than they do the still segment. Hey Canon! I DON'T shoot video with my 7D! Never will!
Because entry level is where they make the most money and that money then gets used for R&D of the higher end stuff and new lenses.
The SL1 is marketed at, well let's be honest, young ladies. It's a small and compact and fits in a handbag.
The t5i is marketed at the beginner, and those on a budget that want functionality and good IQ.
The 60/70D is for the hobbyist and enthusiast, but likely those who find the rebel a bit too small and plasticky. It fits a certain profile. I can't quite figure what myself but I'm sure it exists!
The 7D is for serious photographers who need the speed and durability but aren't pro and don't have thousands in the bank. A poor mans sports camera.
It's all about choice. Why are there 50 types of potato chips? Why not just one pack in one size? Some people are hungrier than others just like some photogs want more camera than others.