Software Engineer here - I objdumped the macos binary and it does look like it's written in Cocao -
Yes, but the kernel isn't really in play here, is it? They might need to write new USB drivers, but that's only part of it. The rest is UI specific- so if you're talking about Android... well the Android UI (which is done in Java) - is very different from the OSX or Win32/64 ui. It's very difficult to go from desktop to mobile OS. It's a clean, ground up rewrite.
Linux, in general, is ALSO not a RTOS. Yes, there are kernel versions that are more realtime than the master branch, but it's in exactly the same boat as MacOS and Windows. Further, the optimizations required for both of those platforms are well known (on a mac it's even easier now). So Linux doesn't really have a leg up on Apple of Microsoft here at all. If it did, I'd be running ProTools on Linux.
Honestly, I don't think there's the support for the platform needed to warrant a port of RM to Linux. It would be cool, yeah, but given that most users of the Kemper are NOT CompSci majors, it doesn't make sense to target a 0.1% platform.
I'd rather see more improvements to RM for all users.
Looking at binaries you wold find traces of UI-libraries from the local OS everywhere. That doesn't rule out the use of higher level abstraction layers.
There are UI-abstraction-tools that even include the most common mobile platforms, although their efficiency may be questionable.
Real-time is not an issue for RM itself, but the reality is that a lot of people use it in a home/studio-environment as an element in a more complex media-creation platform.
The standard linux-kernel is not real-time-compliant, but with the RT-patches it is 100% compliant with acknowledged RT-standards. Even a standard kernel compiled with low-latency-options is a lot better than most of the competition. There are of course more than decent alternatives to linux, but those do not include Apple or Microsoft. Systems that makes it very hard for users to even prevent things like automated maintenance-procedures from interfering with their workflow are far from optimal as a media-platform.
I completely agree that usability must be first priority, which of course makes the most common operating systems first priority too. My point is only that systems could be improved. In the current environment where media is mostly paid by advertising nobody really represent the consumer anymore. If people knew more about alternatives they may choose differently, which in turn could push the major players to produce better solutions. Given the resources at their disposal, I find it almost ridiculous that Apple and MS have not yet come up with better solutions.