@Iggy,
the last generation of the G5 PowerMacs did have PCIe and no AGP slots, up to 4 cores @2.5GHz, and they have a maximum RAM capability of 16gb, not 8gb, so if that model is ever supported by the MorphOS Team, there is the same potential for PCIe video cards to be supported on MorphOS2.x as there will be on AmigaOS4.x with the X1000.
As far as I know the Graphics card needs to have a correct flash version, and the only PCIe Radeon card that's suitable is the 1900XT, it's what I've got fitted in my Quad 2.5, and the last time I mentioned it one of the MorphOS team said that was news to him. (if I get time I'll find it on Morphzone)
