The daughterboard could be an PPC one instead of 060 if one so wishes. It's mainly a PCB routing and assembly pain.
The OpenGraphics project (OGP) is a nice thought but uses high end FPGA where the cost for chips and route-and-place tools is prohibitive. So it's in practice a no go solution. It's better to polish your knowledge in graphics and start from scratch. Do less, do the important and be confident that it's enough (less is more). Are all functions of the PS3 really needed? if not which one would be the most important ones?