> The Marvell Vi still only has two 4 lane PCI-e channels.

Yes. I did not indicate otherwise.

> would an 8640D be a better option than a 1.7 GHz 7448? I'm not sure.

Me too. The L2 cache size is on par (1 MiB). While the 7448 core is 36% higher clocked (1.7 GHz vs. 1.25 GHz), the 8640 bus is 150% higher clocked (500 MHz vs. 200 MHz). What is more important, faster core clock or faster bus clock, depends on the kind of application. (I'm ignoring the dual core option of the 8640(D) here as it would be of no use for MorphOS, which is the context here.)
But I would guess a board without separate northbridge chip is more easily and cheaply developable and producable.

> no one has touched on the other processors I mentioned.

The PPC970(MP) is actually used in Fixstars' PowerStation. And even the PWRficient (that you didn't mention, btw) is actually used in a real product although its (non-)availability on the free market can be considered the same as Cell's.

> Outside of a netbook, what would we use a processor with a built-in
> LCD controller for?

A board designer doesn't have to use the DIU. He can easily ignore it if it's not needed for the purpose of the board.

> Do you have anybody in mind who might be willing to work on this?

None, unfortunately.