It looks like most people are pretty damn happy with their 5D2s... There are just some quibbles about the ancient AF system really. Otherwise, fps, ISO, mp... all up to par. Really, if the 5D2 was introduced last year, it would still make sense in the Canon lineup. If the 5D3 is just going to bump up the mp and ISO a bit and largely leave the AF alone, then I say I'd rather wait another year or so and get a 5D that will have a significantly upgraded AF instead of getting one in the next 6 months that upgrades everything just a bit but still leaves me wanting more. And out another $3k lol. What do you think? Is the 5D2 so terrible now that we need an minor upgrade on things we're mostly happy about right now?
I don't think Canon are going to just up the MP and ISO while jumping the price to $3k. I expect Canon are going to be putting in a lot of effort in making sure that the 5D3 is going to still be head and shoulders above any other camera in it's category eg. D800.
The one thing going concerns do; is ensure sustainability.
One would think that if they made the 5D3 such a superior product, it would cannibalize other canon models, (higher margin offerings) secondly would be hard for them to show improvements in a 5d4 etc. As Neuro would put it, if one plotted the value propositions; it would be close to a second order polynomial , and a very high value 5d3 would be a distraction to the progressive market segmentation they have tried to create.
I suspect they will make it very close to the D800 in terms of a value proposition. Again thinking sustainibility.