I finally reached
https://www.ports.debian.org/ by realizing 'ppc64' is a name of a port. If I continously search 'powerpc debian', I doubt I would give up before finding this right place. However this is potentially what non-G5 users would face, as they clearly know their cpu will not run anything 64bit.
So my 2 suggestions are:
2. Educate visitors, the existence of ppc64 port, along with powerpc port, and clearly states their intended use, in that page.
I'm not sure if anyone with admin right is in this list, if you know someone has, please forward.
Thanks,
Hao