Aros is the only realistic option in foreseeable future
AmigaOS is PPC and will stay in coming years. It is not difficult to forecast because Trevor certainly has contracts regarding his expensive toys (Tabor and X5000) and noone else will pay for ports to another ISA. MorphOS is announced to change ISA but I assume they will support selected AMD64 PCs, not ARM because AMD64 is the most powerful hardware at the moment