I'm not sure why the article is speculating about a "seismic" change. Apple (and Microsoft and Google have followed) has established a pattern for their OS evolution: yearly incremental updates.
https://www.youtube.com/watch?v=ghdTqnYnFyg
It's 2018, 20 years since Apple first announced Mac OS X at WWDC 1998 as a change from their original Rhapsody strategy. The 20th anniversary of the actual release of Mac OS X for consumers is approaching in a few years.
Now, I still believe that there is plenty of life in Mac OS X, and I could see it easily being usable at least throughout the 2020s, provided that Apple maintains it in the meanwhile.
However, I definitely wouldn't mind a new desktop OS. Let's face it: modern desktops such as Windows, Mac OS X, GNOME and its derivatives like Cinnamon, and KDE are all based on the GUI paradigm developed at Xerox PARC for the Xerox Alto workstation. This paradigm was further developed by Apple for the Lisa and the original Macintosh, and it has been further refined by NeXTSTEP, Windows 95, and early versions of Mac OS X. However, there are other GUI paradigms that haven't been tried in desktop environments outside of research labs and niche environments. For example, Xerox PARC also developed the Smalltalk environment. While it is commonly thought of as a programming language, it is more than just that; it is an operating system running inside a VM where everything is an object. This environment could easily be used to write full-fledged applications that also support message passing through a REPL. It is possible to build a system of GUI applications that are scriptable and composable through Smalltalk's message passing system, thus combining the usability advantages of contemporary GUI applications with the power of the command line.
There are other features that we don't have yet that can be added to a new operating system. For example, we came close to having a database file system available for the desktop when Microsoft was working on WinFS over a decade ago, but unfortunately it was cancelled in order to get Windows Vista shipped faster. Having a semantically-rich file system would be a very nice thing.
At the same time, though, given that the iOS platform is Apple's major revenue stream, I am concerned that the days of the Mac are numbered. I feel it is Apple's dream for everyone to be using the closed-down iOS instead of a general-purpose OS such as macOS. I feel Apple has been preparing pro Mac users for this transition by deliberately neglecting the Mac Mini and Mac Pro lines and by turning the MacBook Pro into basically an expensive, "blinged-out" MacBook Air Plus, signaling to pro users that the future of Apple won't include them (although the announcement of the 2019 Mac Pro might be contrary to this view).
All of this is to say that I would not be surprised if we see a new OS from Apple within the next five years, but I'm concerned that instead of seeing the next step of general purpose desktop computing, we're going to see a scaled-up version of iOS instead, which would be disappointing, especially if general purpose desktop computing is relegated to Windows and desktop Linux. I'm of the opinion that we do need another non-Apple general-purpose desktop OS, at least to hedge our bets in case Apple goes all-iOS and to avoid the situation where Microsoft has a monopoly on commercial general-purpose desktop operating systems.