Well, my MacBook runs very hot, it's quite unpleasant.
I simply like to select the best device for the job in hand, I think for portable devices, where processing power is less important than battery life, then an ARM processor is pretty good. Also on a portable device, boot time is important, if I'm on the tube, I don't want to wait 3-4 minutes before I can start working if my journey is only 20 minutes.
On a desktop however, I need it to be fast, boot time does not matter as I never turn it off, and good multitasking is important as I'll often have things running in the background while I do something else.
Another example, I'm a big fan of the IBM i/OS, this is an awesome server OS, but an utterly awful desktop experience (it's green screen/terminal only). So I'll happily use it as a server, but nothing else.
Quite simply some Operating Systems excel at some things but not others and RISC OS is an example of this, it's not powerful or good for anything requiring a lot of horsepower, multitasking is very bad. However it excels at usability, snappiness, and running on low-power hardware, we should play to it's strengths and not always focus on it's weaknesses, which I believe the Iyonix and any successor does.