PPC is dead from a consumer perspective. While there's nothing stopping it from being a hobbyist platform, it's expensive as hell and there's not a lot of hardware to choose from.
X86 is well-supported and cheap, though there's a zillion different hardware configs. Getting it to run on everyone's PC's can be tricky because of this.
ARM is cheap as hell, and there's plenty of real cheap hardware available (the omnipresent Pi and boards like it). The hardware is a bit more uniform, but performance is lower than X86. Still, it's cheap as hell.
I'd prefer a Pi port, but that's subjective.
I agree with the ARM choice but - ODROID C1 (1.5Ghz quad core CPUs and eMMC 4.5) would be another alternative for the same price range but faster and with an eMMC drive capability.
