Well, it would certainly take some modifications to OS9, as well as SS. One big challenge I can see is integrating platinum's window system to run in OSX. It's definitely not impossible- just really really hard. Another approach is to try integrating a PPC interpreter into the classic environment. I'm not really sure that's entirely feasible. But it's interesting to think about. Someone else might have a better answer.
I think at that point it would just make sense to work on a compatibility layer which would make the apps run natively in OS X without emulation (you may be familiar with Wine). There was the short-lived Classix project. It's a daunting task, and there hasn't been many people up to the challenge. But of course that's the ultimate solution. I think if someone used the Carbon API it could have been done somewhat quicker than what was done with Wine.