Qemu is firmly on the trajectory to become an emulator for everything. We are already using it to emulate amd64, arm32, ia32 and ppc32. It would not be hard to make use of its mips32 support too. Thanks to Igor Kovalenko, it very recently became the first open source emulator which can do pre-Niagara UltraSPARCs. The picture shows Qemu/sparc64 current with OpenBIOS current running HelenOS current:
P.S.: It looks like someone is already working on Qemu/ia64, so before too long, all HelenOS ports will be able to run on Qemu, which is just great!