>> I'd like to be sure of the support (or not) of Pcie G5!

> it would be even more wasteful to run MorphOS on quad core G5's than it already is
> to run on [...] dual CPU G5's now.

PCIe-based G5 is not just the quad-core PowerMac G5, but also these dual-core and single-core systems:

http://www.everymac.com/systems/apple/powermac_g5/specs/powermac_g5_dual_2.0.html
http://www.everymac.com/systems/apple/powermac_g5/specs/powermac_g5_dual_2.3.html
http://www.everymac.com/systems/apple/imac/specs/imac_g5_1.9_17.html
http://www.everymac.com/systems/apple/imac/specs/imac_g5_2.1_20.html