I'll bet ATI is doing some hiring of additional engineers right now or in the near furture, to beef themselfs up a bit, so they have enough engineers. however i think ATI can do this.
the GameCube2 and XBox2 GPUs would NOT be the same, as somebody suggested in this thread. they would EACH be tailored to what MS and Nintendo ask for, seperately.
XBox2 GPU would be the highest possible performance that ATI could offer, with enhanced DX10 or DX11 features. We are talking at least R500 as a base, perhaps a souped up varient of R500, like NV2A was a souped up NV20.
GC2 GPU would be more efficient, based more on what the Flipper was (and also maintain compatibility) maybe geared more toward OpenGL 2.0. it also might not have anything to do with R500 or R600 like the XBox2 GPU would. probably a completely different arch. based on the Flipper concept with on-chip memory.