Surely what is needed to sustain development is enugh units being sold. So is there enough of RISC OS 6 availabale to allow manufacturers to build cheaper computers from it? Presumably STD had to pay a substantial fee to make the A9.
As things stand I'd say that even the A9, let alone the Iyonix are out of reach of the majority of people.
Having said that, I think more should be made by Castle of the "legendary build quality" they used to refer to. This has given me the opportunity to continue using a RISC OS for many years and no doubt the Iyonix will still be a usable system for many, many more years when its successor is the envy of most people in the RISC OS community.
To my mind, that's one of the most important parts of Acorn and RISC OS's history, the longevity.