>>> SAM460 [...] (main reason for supporting the 460) allowed to support X5000 boards
>>> (getting it to boot) in hours instead weeks.

>> I'm still interested in technical details on this :-)

> I would venture to guess that adopting a board with a PCIe expansion bus involved
> a learning curve. And that that experience helped with the X5000 port.

I don't think this is about PCIe at all. That's what geit said about the helpful similarities between the Sam460 and the X5000:

"This is what I was told about the reasons the x1000 was off the list, as it is completly different."

The X1000 does have PCIe, doesn't it? Besides, MorphOS has already been shown on PCIe-based iMac G5 about 6 years ago (so way before work on Sam460 support started).