The impression I get is that making RISC OS run on x86 wouldn't be ridiculous. (If you stick to one set of hardware.)
If ROL or Castle had access to the tools Druck mentioned, I suspect they could roll out a proof of concept x86 version pretty quickly. Of course that wouldn't be much use to anyone without any programs.
If such a system were to move beyond the realm of specultation, would a combination of Aemulor and the red squirrel engine be a straightforward solution?