Is modern ARM stuff done big-endian? because AIX is exclusively BE iirc

That, weirdly, should be fine; ARM is bi-endian in the sense of being perfectly happy to run either way. In fact, the easiest way I know of to test software on a big endian system is to run a perfectly ordinary Raspberry Pi with NetBSD's big endian port for it:)

I never said it'd be an easy port, although there was an x86 (and s/390) port back when time itself was new.

edit: s/390 is big endian.