Wouldn't the time be better spent getting Linux to adopt certain RiscOS methods such as the way applications are organised or the way "hidden" files are not needed.
I have just recently installed PCLinuxOS on a laptop and have been very pleaseantly suprised (I gave up on Ubuntu due to issues with my hardware, Nvidia drivers!, and the need to start using the command line). I would recommend PCLOS to anyone looking around for a RiscOS alternate, it even has a window decoration called RiscOS as part of the distribution! Granted PCLOS is meant to look and feel like windows due to the need to
attract those users. However you can easily change all that and right now my PCLOS desktop looks almost the same as my RiscOS one.
The biggest issue I have found with PCLOS/Linux is all those damned hidden files in the users home directory. It's exceptionally messy and very dangerous if non enthusiast users start to adopt Linux. I think this is an area that RiscOS's approach to organising files, folders, applications and configurations can be of great use.
As for applications themselves I don't think there is much to be gained. Some of the smaller apps maybe. A simpler cleaner FTP certainly! The default one is clunky and looks all the worse for having all those hidden files visible! PCLOS/Linux already has a wealth of apps with features that are sadly lacking under RiscOS (a reason for me switching). For example video works! here's a list of some of the apps that come as part of a PCLOS distribution:
Gimp (Image editing)
Thunderbird ( email and news) - Excellant "new/unknown" message handing
Firefox (browser) - version 2 as opposed to RiscOS v1
OpenOffice - office suite that can also read/write M$ if you are peverse enough
Calc - spreadsheet
Writer - wordprocessor
Base - database
Draw - ! yes
Impress - slides multimedia presentation
Amarok - music player
Beryl - 3D desktop manager
Frostwire - peer to peer
MPlayer - video/audio player
FYI everything worked "out of the box". Network setup was perfect and automatic. Wireless connection to my Canon printer served from XP laptop, worked first time. All in all an astonishingly pleasant non windows and totally free experience.
Remember folks all of the above is FREE.
So my suggestion would be to build on top of what is already working and make it better. A RiscOS (PCLOS+ROX+?) style distribution.