The real question is should those who really care about security and are fine with the limitations of an sandboxed app really be defining the OS X ecosystem.
http://fortune.com/2015/10/13/apple-merge-ios-os-x/
(They also said they would not launch a small tablet and so on...)
We know it's not happening because Tim Cook has explicitly said so. Additionally, it doesn't make financial or engineering or UX sense.
Mac OS X and laptop and desktop hardware will become more and more of a distraction. We've seen them stagnating already. As a unix, Mac OS X is a rather elderly BSD.
They may keep a laptop device in the mix, but it will be more like a chromebook and run iOS.
Again, I'm speculating.
[Citation needed]