Except Apple already did this once, and honestly the under the hood bits are mostly fine. Virtually all the bugs that people complain about are in userspace programs, like Mail, Safari, or especially Finder. Using a different kernel and switching form BSD to GNU under the hood isn't going to fix any of that.
If Apple made a new OS, using a Linux kernel, and getting rid of the NeXT framework stuff (no more Objective C bullshit, no more deprecated Carbon, or Cocoa/ObjC/Swift), I think it would work pretty well.
Many major issues regarding security,filesystem keep cropping up(there are a couple of links in the article). The idea is that instead of spending time and effort trying to maintain the OS, they can instead use the battle tested linux and focus exclusively on the distinguishing features.
And this will hopefully enable Apple to focus on the issues in the userspace.
