A/UX only supported m68k macs, right?
I wonder if you could patch the m68k emulator in the later nanokernel for PowerPC Macs to support it. Would it be legal? Gods no. Would it be a throwback to the kind of really dirty hacks I associate with the 90s? Absolutely.
It looks like a decent amount of work reversing the Powermac nanokernel has been done: https://github.com/elliotnunn/NanoKernel