It is likely, at least in my mind that Canon may not want to take the risk of making a 1Ds or 1D the first product with a DIGIC V - although maybe a Powershot G13 could also fulfill that requirement. *grin*
It may also be necessary to bring a new generation of DIGIC processor into mass production first in order to be able to deliver the chips cost effectively for a 1D or 1Ds platform.
All conjecture of course!
Canon has always introduced their new digic processors on 1 series cameras. Then they trickle down the new technology to the lower priced cameras. There is little risk in doing this, even if a catastrophic issue happens, they do not produce many of the high end cameras and can retrofit them all. They have plenty of profit $$ to work with.
However, if the same thing were to happen to a point and shoot sold by the hundreds of thousands, then the risk is higher, there is only a tiny amount set aside for repairs and maintenance, and a replacement would cost about the same.
Most introductory issues are solved by upgrades to the software. Software upgrades can even work around hardware issues, so after the years of development and testing of a new processor, the risk of something big going totally South is very small.