I doubt that "big outfits" such as Microsoft would be the least interested in RISC OS, much less so to simply kill it off. It's not as if RO poses even a minimal threat to any of Microsoft's markets and the market share doesn't even show up on measurements in the UK, let alone the world. The only thing I see that MS and others might be interested in would be the font rendering technology and even that may not be worth much anymore.
There's hardly anything "groundbreaking" in RISC OS anymore, most operating systems have cought up and moved way beyond what RISC OS has to offer. Even SkyOS seems to have outpaced RISC OS feature wise and that has been a hobby project up until now. So if the IPR is for sale those most likely to want to buy it would be some company already with its business tied to the OS.