Canonrumors.com has a tip on the testing of a new video DSLR. Details are a bit vague, though they focus on problems with moire.
The 7D (and 5D) all suffer from moire to a greater or lesser extent because they are scaling the image from the chip to 1920x1080 on the fly. They "get away" with these problems partly because of the other advantages of these cameras (including price.) But if Canon actually came out with a "video" DSLR - and charged five or six thousand for it - then they'd have to solve that, and a few other problems.
Of course, in the mean time, we're still waiting for the new video camera Canon has already alluded to.