I think that source is a little bit confused on the distinction between iOS and OS X (macOS?).
iOS and OS X share the same kernel, named XNU (it's the userlands of the two that are almost completely different). That's been the case since iOS 1. Whenever either OS X or iOS gets ported to a new CPU (or CPU subfamily), the kernel gets another set of macros added to it for the purpose of identifying the new CPU. The presence of a new ARM macro in XNU doesn't mean much at all - it already has a ton of them, as well as truly ancient macros from long-forgotten systems (m68/88k comes to mind). Those macros have nothing to do with OS X or iOS individually - they're relevant primarily to the kernel itself.
Every now and then Apple release a new product, like TVOS for the Apple TV and people ask why Apple wrote an entirely new OS. why not base it on iOS or OSX. of course that's exactly what they do. There's a common core to OSX, iOS and now TVOS that are almost entirely the same code base. Which specific files are common or different for each flavour probably changes from time to time and this may well be a case of that.
The fact is though, iOS and OSX are already as much the same code base as they can be, and as much different as they need to be. That balance may change as the OSes evolve, but I don't think there's any pressing need or benefit to converging them completely.
The necessary divergence you talk about is mainly the UX coming from different input methods for the pointer device, correct?
With the (partly regretable) adoption of UI design patterns that are mainly meant for touch devices, such a merge appears to be closer however. I think the main patterns missing are
* a more powerful touch-capable tiling window manager
* a method to get "mouse hover" events working on touch devices. finger hover?
* a both touch- and precision pointer friendly implementation of the OSX menu system.
I'm not convinced that employing 3D Touch to do the typical things of mouse hover is a good idea. Displaying help text to users being lost when they do a very specific gesture? It needs to be something that every user can immediately pick up on.
Maybe a stare-o-recognizer using the camera? If the user looks puzzled at a button, display text to explain ;-).
In and of itself that doesn't prove anything. That file has had symbols for multiple architectures since forever, including CPUs like M68K, Sparc (years ago, I had hoped that Apple would buy Sun instead of Oracle - oh well) and VAX (but not Alpha).
iOS and OS X share the same kernel, named XNU (it's the userlands of the two that are almost completely different). That's been the case since iOS 1. Whenever either OS X or iOS gets ported to a new CPU (or CPU subfamily), the kernel gets another set of macros added to it for the purpose of identifying the new CPU. The presence of a new ARM macro in XNU doesn't mean much at all - it already has a ton of them, as well as truly ancient macros from long-forgotten systems (m68/88k comes to mind). Those macros have nothing to do with OS X or iOS individually - they're relevant primarily to the kernel itself.