Been running ELFv2 BE ABI since 6.2-rc1 on my G5 11,2 and Talos II and it just works. Kernel and module size is a bit smaller due to lower stack usage it seems.

ELFv2 BE ABI 6.2 kernel is also possibla with clang with use of yet-to-be-mainlined patches (see https://github.com/ClangBuiltLinux/linux/issues/1761). Performance seems on par but with some Altivec regressions compared to GCC build.