powerpc64 backport to g5

Hi,

Now that POWER9 systems are pretty well supported, I'm setting away some time
next year to backport powerpc64 to the Mac G5.  Is there anyone already doing
that?  I already tried this once (based on the macppc sources) but failed.
I don't want to throw the little that I learned out the window.  I'm giving 
myself more time next year than my last attempt.  Right now I'm dreaming big, 
but I'll need to awake to do some work on this.  I'll likely start in
January or February with compiling on G5 macppc arch and testing on amd64 under
qemu.  Please don't give me any kudos until I share something that works. :-)

Best Regards,
-peter