Its no good just porting the OS to something unless we have a clear idea on what it will be used for and vibrant software market to provide suitable applications for it. Otherwise you have an iconbar on the bottom, a cog on the corner, and the question on what on earth do you do with it now?
Devices such as UMPCs which try to be full desktops in a vastly smaller form factors just don't work. Its very frustrating coming from the same application on a fast desktop (or laptop) to using it on much slower device, cram on to a tiny screen, and needing the dexterity of a brain surgeon to use the touch screen or minature keyboard. If you want desktop style working you either need a large laptop for use on the move, or an A9 which you can plug in to a full sized screen and keyboard when you get to where you are going.
What works far better are applications targetted at the types of things you need the device for, and use way of achieving it matched to the smaller device. Whilst the spec's of Apple's iPhone are poor compared to most other smartphones, the applications and easy of use have set new goals for everyone. Compare the experiance of rubbing a couple of fingers over the iPhone's screen to do things, to having to use a fiddly stylus on a Windows UMPC.
So just what RISC OS applications would you use on a small form factor device? Our best apps such as Artworks, Photodesk, TechWriter, Ovation Etc, aren't the sort of things you'll use with a tiny screen. You'll definately want a web browser but we haven't got one of the capability of Opera on the desktop, never mind the additional features of the mobile version to work well with small screens. Were also is the ability to synchronise email, calendar entries, and to do lists with a desktop?
If we still had a huge pool of software writers willing to creare innovative applications to exploit new devices, then it would be worthwhile. But its obvious from the desktop market these people aren't around anymore, and its unlikely to interest them enough to come back. I'd like to be more positive, but I can't. We've all too old, been kicked when down too many times, and here is just not where things are at anymore.