I think we'd all have a better time if Apple would let us run current versions of xnu with only Darwin without having to piece everything together to end up with a system than might work but just won't because xnu is proprietary. I think there are valid cases where Darwin can be a more attractive choice than Linux, but there's just no interest because xnu is unattainable, and the alternative is using a Hackintosh kernel with degrees of stability rather than it being straight up rock solid stability. I don't mind the requirement of Macintosh hardware, but that isn't good enough for Apple, you either take the whole system or nothing (or live vicariously dependent on a few intrepid kernel hackers).