I'm a great believer in not re-inventing the wheel....unless it's square! So take what already exists and works well and improve it. I get the distinct impression from the Linux world that Ubuntu is being hyped up and PCLOS is gaining ground due to its flexibility and greater hardware compatibility. A darn sight easier to configure as well I might add (I abandoned Ubuntu). So my suggestion is for a PCLOS distribution with RiscOS improvements, especially the location of those pesky hidden files. RiscOS sticks them all in !Boot, which is far far superior home for them (or should that be /home )
Mind you I noticed somebody mentioned GOBOlinux, I need to investigate.
Also note you don't want some distribution that lives amongst the enthusiasts. You want to affect the mainstream. We know RiscOS has features that are far superior to the existing 3 so wouldn't it be good to have those features adopted by linux-world ?