iOS (ARM)<> MacOS (x86). At least for the moment.
I'm guessing an iOS port would be very hard indeed, legal stuff aside, because iOS runs on a very limited set of machines, which means almost 0 chance of getting drivers for any other one. Even at the CPU level, if Pi is not implementing some optional ARM feature that Apple has, you're toast. And it gets worse for the non-CPU stuff: GPU, peripherals... Look at the hard time the various Hackintosh communities have with finding hardware that will run MacOS, and MacOS does run on a lot more hardware than iOS to start with. Would be fun though. We could call it Hackipad, or HackApTV.