The RO GUI is the most flexible I know. However, hardware is not up to modern PC standards anymore, which has simply resulted that those types of software that rely on such hardware, have not and could not appear as well.
What is the Iyonix (and arguably A9home) hardware capable of -- web browsing, e-mail, word processing, DTP, audio processing, a bit of media playing, perhaps video chat, etc. However, our current software standards (arguably due to the state of market) can only provide just about half of that capability, though in a fine way.
So, there's my reasoning. If you can happily live within those software boundaries, partially due to hardware limitations and partially due to market size, you may enjoy a wonderful (British!) computer with one of the finest GUI's ever devised.
If you can't live happily within those boundaries, I find it a comforting thought that it will be highly likely that we may soon enjoy our superb GUI, with some of its terrific software, through a Open Sourced emulator. Even though I strongly recognize it's still very much in an early stage, the fact that it's GPL means that it may have a very interesting future.
One idea I've been toying with recently, similar to the way Apple chose. That is, to take the best of RISC OS, and put it on top of a solid modern OS core. Similar to what Mac OS X represents. Again, it will definitely not be easy, but it could provide a viable way out the current dilemmas.