Personally, I don't care if there's another version of RISC OS to contend with. If it's regularly developed, openly; moving forward and easy/cheap for users to migrate to it'll become the "standard" version *very* quickly.
If the options are two stagnant branches, or two stagnant branches and a developed one; I know which choice I'd go for.
To prevent multiple forks, proper community and leadership which listens and responds constructively will be required. No, it won't be as big as Linux, but looking to see the problems and successes there will be helpful in setting up an open RISC OS.