I would love this to be true. However, it sounds too good to be true. I have read too many false rumors and so many unimpressive new products since 5D mark II that I have a large grain of salt.
There are two ways this could be spoiled:
1) this does not happen
2) 5D mark III is not even close I (among the other HDSLR people) would hope it to be (e.g. Having Digic V, fixing the aliasing and resolution problems on video). I use the 5D mark II for video about 80% of the use, so the video section plays the most major role in the choice to upgrade or not to upgrade. I have shot ~10 terabytes of original footage with my 5D mark II.
The latter could happen if the camera is pushed out too early and the essential upgrades are descoped like have been the case with 7D, 550D, 600D, 60D. I am sincerely hoping that it takes so long for Canon to update 5D mark II because they want to make it perfect. The hopes are so high for the 5D mark III that they better fix the video problems before they release it, delaying is better than releasing without improvement. If the severe video aliasing and moire would still be in 5D mark III, I would give up and continue with the 5D mark II until I can afford RED somewhere in the distant future. I don't care how many autofocus points, optical viewfinder or anything like that, 5D mark II is perfectly sufficient for still images. In still photos, 5D mark II does everything I want and I can concentrate on trying to make great pictures rather than to the tool I use to do them. However, for 5D mark III absolutely essential: I want professional cinematic image quality on my video footage instead.
So I hope that when a 5D mark III rumor comes true, no matter when (now, later, distant future), it holds to the anticipation this model will have on it. The need for serious upgrade on the video processing side is such that I hope that Canon listens and acts for it. The camera has huge potential but as it is now (all models), they are all deeply flawed, they produce deficient footage and lots of effort is needed to avoid e.g. the aliasing problem and very often footage is ruined by aliasing and it can be only noticed afterwards when viewing on computer. 5D mark III - the choices are: 1) no more aliasing 2) no more Canon.