Another question is, how much would it cost to port AOS4.1 to Raspberry Pi?
Given that most of the OS developers work out of a sense of passion rather than desire for a salary there's no way to know. The whole codebase is in C now, so in theory it's easily portable. The technical challenge is drivers for the Pi's onboard hardware (graphics, networking, USB, at a minimum). The bigger (and, in all likelihood, insurmountable) challenge is Hyperion giving it the go-ahead.
Would big-end and little-end be a tough obstacle?
I don't know enough about this issue to offer a viewpoint, so... maybe? The extent of the difficulty probably depends on whether or not there'd be a PPC compatibility layer.
I would pay 100 u.s. for a license if it meant having more hardware choice.
I think it would increase fan base many times over.
Agreed. Even if 99% of hypothetical OS4 RPi installations were pirated it would probably still amount to greater revenue than what they're making currently.