I've not been involved with RISC OS for some time now, but maybe now is the time to very seriously look at using the wealth of existing ARM hardware out there. I don't see a lot of point in an Iyonix II, which would almost certainly sell worse than the first one, and look even more out of date compared with Macs and PCs available. Sure a better alternative would be to tap into the area of computing which is growing massively, the tiny little laptops like EeePC, or one of the alternatives which has an ARM processor (of which there are a few).
In this market, buyers have shown that they're not necessarily all that bothered about getting an OS they have heard of, and of course, the multimedia failings of RISC OS are less relevant as I don't think these machines are getting used for watching HD movies and the like anyway.
The of a good web browser and actually getting RISC OS to work on such hardware are major roadblocks, but I think it's a better option than creating a desktop computer that almost nobody will buy.
I'd never buy another desktop RISC OS computer again, it's just not useful, but a little laptop for taking on train journeys etc. that's a real possibility.