Well, I really just couldn't resist a joke, but...
I
was under the impression that every PPC chip Apple used was big endian. According to this
Wikipedia entry, apparently some were for lack of a better term "bi-endian", able to switch back and forth; but were restricted to one mode or the other by the logic board. So today I learned something.
Another
discussion I found on the topic seems to confirm that notion:
"I think it's probably fair to say all the Apple devices that shipped were big endian as the OS and firmware were, and while in theory the 32-bit machines could operate in little-endian mode I don't know of any distributions that actually did so, and 970 didn't support it."
As mentioned in that quote, I think you're right about the G5/970 being big endian only, which seems to be confirmed by another
Wikipedia entry.
Didn't expect to need some schooling. Guess that's what I get for trying to be funny ?
EDIT #1: Seems I've heard of OpenSUSE being run on PPC too, but I'm pretty sure a ppc64le version isn't going to work on any PPC Mac. Perhaps there's another version available out there somewhere.
EDIT #2: Yes, seems OpenSUSE can be made to run on G5's at least:
en.opensuse.org