How would a Canon 7D-5D Best of Both World's enrage?
From the 7D - better weather sealing, more FPS, better AF
From the 5D - FF, Better High ISO, Better Low Light, Better IQ
Added - Large Resolution, some other bells and whistles like wireless built in, articulating screen, Dual Card etc.
Only downside I see to this is some of the 7D users loosing the crop/reach of some of the lenses and the EF-S lenses not fitting, but could also see maybe the 70D becoming more of stepping up to be a high FPS top-of-the-crop to fill that void.
Compared to the D800, the Canon 5D7D would be Faster FPS, maybe a little less AF, Better ISO especially at the top end... expect 12800 Native, and cheaper. The D800 may produce larger pics, but I think the 5D7D, especially paired with something like the 70-200 F/2.8 IS II would produce better IQ images at pretty much every level.
You're forgetting human nature... some people will bound to be ticked... especially if the consumer base cant use their ever so expensive ef-s glass on this beast. Another thing to ponder... I wouldn't mind dual card slots (granted I hardly ever get to the point where my card runs out and i cant swap them out, I can see when they could come in handy) how many would want the CF and SD combo like the D800 or would you prefer a common size like both SD's or both CF's? I think I would prefer the same dual CF's... keep the same speed, both be umda cards... can SD cards keep up with umda CF cards? if the CF ran out and the SD kicked in and my buffer all of a sudden started filling up quicker I would personally start to get ticked.
Having crawled up from the EF-S ranks, outside of the 10-22, there really is not much to speak of. In fact lenses like the 18-135 probably hurt more than they help.
But again... I could see the 70D becoming the King of the crops... May not appeal the most, but give some of the 7D users better ISO, less noise and more resolution and they may be happy.
As for the Dual card, I would say Dual CFs or CF and then the new XQD. Not sure if the XQD will catch on. I have only filled a card once, and that was when I had an 8 card in there because I was importing my 16 into LR. I think SD is a step back performance wise, and would hate to have to drop down from my CF to SD.
Ultimately I am not surprised for Canon to wait a little. Gives them time to tweak, and one-up.
After all, if I were Canon, I would rather and release a better camera two months later and then live with that better camera on the market for 2 plus years, than be out the gate 2 months early and be passed and then have a lesser camera for 2 years.
Really depends on what Canon does. To me the 1DX has a slight edge on the D4. May be some bias, but I think the ISO is better, it has larger resolution and I think offers more. Biased? Perhaps. But I think the 1DX will be a low-light beast and the D4 much noisier.
I think Canon will release the 3 line. This will be a MP Beast, maybe only 4 - 6 FPS, Little less AF, but better ISO and priced a little higher than the D800. So more MP, better performance, better IQ especially in low light.
I also think they will release an update to the 5D. Only slight increase in MP (24?) either the 7D AF or better, maybe 5 or 6 FPS, but in short, strengthen the weaknesses of the 5D line which really comes down to AF, add some improvements, and let Nikon have MP and beat them everywhere else. The Canon would be cheaper, better performing except in size and be a significant upgrade.
1DX > D4
3Dx > D800
5Dx > D800 / D400
Especially if the next 5 series camera performs well at ISO 3200 and higher and has improved AF, Canon will have camera at either end of the D800 that perform.