Ok I took a look at GOBOLinux and it looks like the solution is already there. There are a number of flavours that people have built which brought together into one distribution would be what is needed, specifically:
1. A filesytem organised more tlike RiscOS (they actually based it on Macs)
2. Somebody has GOBOLinux with ROX (riscos filer)
3. Somebody has Gobolinux on an Xscale (!!!!)
4. Somebody has GOBOlinux with beryl
Number 4 presumably means that compiz-fusion should be possible. All of this would enable you to have a very RiscOS functioning desktop and filer. In addition compiz-fusion would knock the socks of any presentation that Windows and Macs can muster.
So it seems to me that the starting point could be GOBOlinux with ROX and then get RiscOS apps added to that distribution.