If they make OS4 run on PPC Macs, I will definitely buy it, and many others are ranting about a PS3 version.
Hardware is the key if Hyperion is going to be able to pull this one off, so I expect a port some piece of HW that is less nieche-ish than the SAM or A1-boards.
Things like the SAM boards will always be there because of their geek factor, but I doubt they'll be enough to keep an entire platform alive.
On the other hand, RiscOS is still around. :-P