I agree about getting RO onto other ARM based devices, very important to offer more choice.
Linux could be made to boot as fast as RISC OS, simply because it can run on much faster hardware. My Sun boots (Solaris) slower than my RPC boots RISC OS, but not much, and it's pretty slow by modern standards.
Mac OS X is a front end on UNIX, and that worked out pretty well for them, obviously they have billions of dollars and brilliant programmers though.
I honestly don't get why people get so worked up about it being on ROM, it's so expensise in such low quantities, and although it can be more reliable, if you have disk failure you've lost access to all your files/apps anyway, so you're not much better off than if the OS is on disk.
Practically all (non-embedded) computers hold the OS on disk, including the most reliable computers on earth like mainframe,UNIX,non-stop,VMS etc. If we have more problems than everyone else with disks, then we should look at fixing it.
Not sure why X is so awful, it's certainly much faster than RISC OS with a decent graphics card, and there are loads of good toolkits, all of which open a can of whoopass on the RISC OS WIMP.
If we are serious about getting RISC OS onto other hardware, and seriously improving it, we should talk to Castle/ROL first as they (well at least one of them) has access to the RISC OS source, and of course have loads of experience with RISC OS. We should make it clear that RISC OS should be made to run on other ARM machines, and ROL cannot go on developing for ancient hardware.
Reproducing the Acorn experience: I suppose you'd need to define what that was first. Although we'd certainly have to make sure no good web browsers ran on it!