What would be the motivation for Apple to do such a thing? MacOS is already a Unix, with a BSD-based userland. Also, they are doing active kernel development - as in architecture development - to enhance the system security, so that even root cannot compromise the system. One part of this is moving kernel extensions into user processes thanks to the fact that Mach is a microkernel. They couldn't do that with the current Linux architecture.
Not only can you do it with Linux, a lot is already done; with SELinux, apparmour, grsecurity, PaX, qubes.
They'd also save on kernel development AND get docker and a lot of other goodies.
Not gonna happen. They already have a unix based OS (Darwin) that supports their Arm and x86 devices.
It's as likely as Google switching to the NT kernel for Andorid
Windows kernel is actually more suitable for Android than Linux kernel. In such an environment, JVM could have been the entire userland.