The Rpi is fantastic for running simple, light altearnative OSes. RiscOS for example runs great!
People tend to load a heavy, unoptimized Linux distro souch as Debian and say "this hardware is slow: it's crap!". But that's a stupid thing to do with a device as the Rpi, in my opinion.
Just test Risc OS on it and you'll understand what I say.
AROS people can chose to ignore the Pi, but even then it will become a Risc OS platform, with Aemulor providing native 26-bit software execution, i.e great Accorn Archimedes programs, demos and games, and AROS will have lost a GREAT opportunity to expand into new, cheap, fixed hardware.