PearPC is basically abandonware, the principle programmer died and Apple abandoned IBM PowerPC chips. The project hasn't had an update in 3 years. The big issue wold be replacing the pseudo OpenFirmware with uBoot and dealing with the video driver issues. The OpenFirmware code that is in place is ugly but the video poses a bit of programming issues.
All this could be overcome of course, but the only people interested in an Amiga OS4 emulator are Amiga folks, probably numbered in the hundreds, most of whom are not programmers. We don't have the resources. The people capable of doing it are not interested, at least not for free...