Something that everyone here is missing is that Canon knows how many 1Ds's it will sell, as all of us who have ben buying them will continue to buy them. Obviously I won't buy another mklll but am on the list for the IV at my local camera store when it arrives. I suspect most of us pros are in the same boat, as are the rental houses, design studios and other commercial users who will be upgrading using the nice tax incentives we get for equipment upgrades.
It would seem to me that the mklll sales have already been heavily cannibalized by the 5D, so upgrading the 5D first will totally undermine any future potential 1Ds Mklll sales. Production lines have to produce, and as a factory planner you have to know what your production lines need to keep them moving. Would you want to be spending all that time and money producing the mklll that will sit on shelves, and be sold off as remaindered items at huge discounts because your own product at almost a quarter of the price has kicked it off its perch? Makes no sense to me, and for that reason alone I'd expect (and hope) to see a 1Ds mkIV first (soon).