The new generation of ARM processors are quite capable in the area of multimedia. The newer XScale models have WMMX which can be seen in action on recent Pocket PC models. DIVX at 640x480 run smoothly on those platforms without skipping frames. Texas Instruments even added a real DSP to offload stream processing and NVidia is now stepping up to offer special video chips for ARM processor that can handle both 3D as MPEG 4.
ARM has also kept its focus on the area of multimedia and has built the CORTEX A8 which has multimedia support and runs about 10 times faster than the Risc PC I am typing this on..
It is that the hardware developers like Symtec and Castle need a lot of time to develop hardware and adapt RISC OS for that platform.
If you would look at Toradex you would find that a complete ARM platform with XScale PXA270 at 520 MHz only costs about 100 euro's. That is because Windows CE comes with a platform builder. The OS can be configured for a specific platform and that helps developers of new machines tremendously.
On top of that Microsoft has a geniric platform emulator on which software and hardware can be emulated so that developers can test their configuration before it is built..
These platforms also support Linux. Not because it has all those tools that Microsoft provides for developers but because it is opensource.
One of the biggest blocking issues in the development of RISC OS seems to me that there are plent ARM based platforms with up to date hardware but noone can use it in conjunction with RISC OS.
Either the platform gets an opensource HAL which would allow other hardware to be used or the entire OS should become opensource.
Remember that the GUI and all other desktopcandy is not to OS. These can still all remain proprietary. For example if Castle would openup ist HAL entirely (provided it caters for all the hardware access in general) there would be a chance that we could port this to many other ARM based platforms.
Just off the record, I have a Netwinder on my desk for more than 7 years now. It has a StrongARM but otherwise pretty much a PC like internal structure. Linux supports most of this hardware so it runs Linux. It could have ran RISC OS if the hardware was supported but unfortunately it is not... To try and run RISC OS software I have been working on riscose under Linux but there was too much work to be done for that to work. The basic structure for running RISC OS apps natively has been added to the Linux kernel and is still there after all those years.. Unused I am sorry to say.
For both RISC OS Ltd and Castle the licensing of the RISC OS Desktop could remain and their profits could even go up...