Yes, that is the idea. Brandy can fairly easily be modified so that the SYS command makes a call to a library routine that can be provided by ROLF. I expect QEMU can be just as easily modified, for compiled applications.
The task then boils down to mimicing a useful subset of RISC OS system calls (SWIs) so that real applications can be run.
While there are many system calls that would have to be implemented to make up a full environment, many, especially the lower level ones, won't be used by the kind of user application that people are likely to want to run so, hopefully, it's not an impossible task.