As Flake stated, people are interested in the 5DIII in part because it's been a while since the 5DII came out. The assumption that a 5DII replacement will have '7D build, AF and speed' is unwarranted, because Canon will need to differentiate the 5DIII from the 1D X on features to justify the price difference of ~$4K (or they'll minimize the price gap and charge $4K for the 5DIII but I really don't see that happeneing). So, people won't get their 'dream camera'.
I'm sure that Canon will want to find some way of differentiating between the 1D X and a future 5D MkIII, but hobbling the build an AF is likely to lead to trouble. I think that current 5D MkII owners are more than a bit annoyed with Canon that there have now been a succession of much cheaper cameras with better AF systems. In addition, the 5D MkII is not regarded overly well in terms of weather resistance compared with say, the D700 (not so great for a "landscape camera"). A 5D MkIII will be up against a D800 and I think that quite a few 5D MkII owners and potential upgraders, will be reconsidering their brand choice if the 5D MkIII fails to address some of its predecessor's weaknesses.