I'm fine with any CPU architecture, x86 or ARM or whatever. The single most important thing is perf/W, and to some extent price and availability. Compatibility with closed-source binaries is something I don't care about at all - it would be nice if Pandora 1 PNDs work without emulation, but that's not absolutely necessary since about everything in the repo can be recompiled quite easily (you would lose assembler optimizations though). I don't care at all about being able to install Windows natively on a Pandora 2, that is something I wouldn't want to do.
In terms of price: I think $500 is quite cheap for a mini-laptop. You can pay way more for a decent normal laptop, and although that one will have better performance, it lacks features like super battery life, being a handheld (pocketable, no need to bring a backpack), dual SD slots, built-in gaming controls, etc.