All the hardware detection would need to be rewritten and all... it would be almost as much work as it was to first make knoppix.....
Mac hardware has standardized a lot over the years. I don't think hardware detection would be that big of an issue. Heck the new G3's use PCI and pretty standard memory. With USB rounding out the mix, I can't see this as too difficult.

Any PPC Linux users out there up for the challenge? I wonder what Klaus has to say on the topic.