my guess for specs is:
improved AF (similar to 7D-quality)
single or CF+SD card slot
still plenty of video options
the 7D will probably come up in specs in the next iteration to maintain its difference from the 5D line, my guess is
perhaps also a new AF system
definitely CF+SD dual slots
I agree that there will be a 5DIII and a 7DII. But, I disagree on the particulars.
It seems clear that Canon got burned by the 5DII cannibalizing 1DsIII sales, and they'll avoid that this time around. The 7DII is a bit easier, because of the APS-C sensor. They give it a pair of Digic5's, maybe a Digic4 for AE/AF, a slight AF bump (maybe more f/2.8 points and new algorithms), same 8 fps, and the 'big' story is a new 21-24 MP APS-C sensor.
The 5DIII is a bigger challenge. It will certainly have more MP - probably 30+. Because that 'sounds' a lot better than 18 MP, they'll need to incorporate some significant handicaps compared to the 1D X, especially since it will have sufficient MP for an APS-H-size crop with more resolution than the 1D IV. They can't knock the video - likely that will be slightly better too, with 1080p at 60fps. So - what's left? Unfortunately, the obvious features to differentiate on become frame rate - likely a slight bump, to between 4 and 5 fps, but no higher; the other lacks will be weather sealing and the AF system. Since the high MP count can be pitched as studio/landscape use, where AF is of less importance, I think those hoping for a 7D-like AF will be disappointed. There will be a few more cross-type points (5? 9?) and they may make the 6 invisible points selectable so they can bill it as 15-pt, but no zones, no spot AF, and no sophisticated customization, and no better in low light. Many 1-series users ended up shooting with the 5DII instead; most of those can live without weather sealing and high fps. If the AF is too good, with a higher MP count as well, the 5DIII will take a bigger bite out of 1D X sales than the 5DII has out of 1Ds sales. If Canon didn't give 1Ds/1D users the perfect camera (high MP, high fps, great AF), it's pretty unlikely they'll give it to 5DII users.
Just my 2Â¢.