thegman: "I think killermike is quite right, it's probably just as easy, if not easier just to rewrite the entire OS, or build it on top of an existing kernel. Of course this has not happened yet, although there is no technical or legal obstacles. It would take a group of very good programmers a long time, yes, but there are many examples of os-rewriting success."
Yes, but let's look at those examples. There are various BeOS rewrites and BeOS-inspired projects, mostly because the community regarded it as abandoned (despite some commercial continuation of the product), valued various parts of the architecture (which is a lot better than RISC OS), and saw that alternative platforms might not offer solutions that could be considered competitive, although faster hardware and improved alternatives have eroded its advantages. There are some AmigaOS-related projects, undertaken for mostly the same reasons, but arguably with less justification. Even Windows has at least one imitator.
But for all these projects, one major thing they seem to have in common is the stream of applications ported from GNU/Linux or other platforms, as the developers attempt to show that their project has real-world value. The original BeOS had its differentiating features and applications, as did the AmigaOS, but those applications - even if available on the successor platforms - seem not to be compelling, nor are those platforms seemingly producing innovative alternatives to things like Mozilla.
So even if RISC OS got reimplemented, what would the benefits really be? In a sane world, you'd end up with something like "GNU/FreeROS", where the "FreeROS" makes up very little that couldn't be done by Linux or other Free Software operating system solutions.
The problem facing the average Drobe regular is that a continuation of today's RISC OS isn't any better than the first cut of "FreeROS" - a relatively stagnant development scene with aging applications and poor architectural choices - but I suppose the latter would at least be open enough for people to improve, integrate, and have it compete and collaborate widely with other systems, rather than be saddled with a artificially constrained corporate roadmap.