I am not saying that Canon would be (or should be) abandoning completely the ISO and DR (sensor) improvements, and we probably will see improvement in both areas, but that is probably not the greatest selling point.
Not the greatest selling point for whom?
They may not realize it, but even for the theoretical "video only" user, sensor improvements will probably benefit them greater than any other single area.
The reason I bought the 5D MK II was the low light performance and reasonable pixel density. Certainly all the features are important, and everyone buys for a different reason or combination of reasons.
The only thing that would make me want to upgrade my 5D MK II would be noticibly better ISO and DR. if everything else remained the same, I'd upgrade.
My point was that sometimes there are very large expectations for the 5D, which will probably never materialize, certainly it will not be a "Lord of Darkness" and will not offer MF DR (nor does it need to).
The 5d appeals to a large user base - which is perhaps its greatest selling point, and my expectation for the next gen camera is to offer greater improvements to the video oriented user, while offering smaller improvements to the stills user (since the camera is already very good in this category).