Apple couldn't choose Linux as a core of OSX or iOS even if they desperately wanted to, because GPL would expand to entire "collective work" including closed-so

Apple couldn't choose Linux as a core of OSX or iOS even if they desperately wanted to, because GPL would expand to entire "collective work" including closed-source userland tools (if they are distributed together with a kernel as a single downloadable and installable package). If Linux kernel would have been licensed under LGPL, or CDDL, then it would be possible. But GPL is too viral for such thing to happen. It was specifically designed to crash the barriers of closed source code and expand itself to entire derivative or collective works.