OS4 - No, Hyperion aren't interested in porting to Macs because that would make sense and give people a cheap path to entry.
MOS - No, MorphOS isn't being ported to G5 Macs yet (or, allegedly, for the foreseeable future.)
AROS - Any Linux that supports powerpc64 architecture should be able to run AROS hosted. One assumes it could be ported to OSX, but I don't know if anyone's done that.
