All the commentls about open source imply that RISC OS would be made into some sort of freeware. But this doesn't follow.
The sources could be made available, without giving the OS away for free. The licensing for the OS could remain the same as it is currently. But it would still mean that modifications could be made more easily (and presumably distibuted as patches, and if appropriate included in the main distribution).
It would still make it easier for different hardware to be supported.
With respect to RISC OS on other architecture, I think that would be OK as long as the system included an ARM emulator.
Programs would still be arm code. Modules could be either native or ARM, the OS would be native.
I believe this would protect the potential for native machines, since all programs would remain compatible.