> So you claim that it's not easier to do on X86 ?

Yes.

> At least I'm unaware of a non X86 AROS port which supports Mesa3D/Gallium/NVidia

"Mesa and gallium have PPC paths already implemented - I think they are used for PPC Macs."
http://amigaworld.net/modules/news/article.php?storyid=5688#76373

If it's there for AROS on x86 and for non-AROS on non-x86 then I conclude that it's not more difficult to do for AROS on non-x86 than for AROS on x86.