I'm afraid I don't really see much difference between my proposal (with the F-I options) and your "version of RISC OS, that ran on standard PC hardware".
The only ones I can think of are that my solution doesn't include RODL, and allows enthusiatic software developers to make a contribution. Who knows, if it works well, it might convert some non-RO people, as well.
OK, modules and other low-level system calls, vectors, etc. will not be usable, but it wouldn't be impossible to add equivalents under the new system.
I think it's selling points would be its small size and consistency of use; I'd like it to work well with a simple frame buffer and excel with meatier hardware.