A number of people responded in the comments including this comment by a fellow named Bryan Mills:
It would be correct to say that OS's using unix-clone kernels have taken over, but not Linux. Linux has most of the cloud and server market, but little of the mobile device and desktop markets. Android has a linux kernel but is otherwise not a Linux distro like Ubuntu, Fedora, etc. iOS and MacOS are both based on the XNU kernel, which is based on the BSD unix variant. Windows still has the corporate desktop market and virtually all of the home PC market except for Mac. It's impossible to know the exact numbers because nobody is counting Linux installations with any degree of accuracy. All of the articles comparing mobile sales numbers to desktop sales are bogus, because mobile devices are mostly cheap disposable devices getting maybe 1 year of use.
My response to this comment is as follows:
The trouble I see with many tech site predictions about which devices will rule the future is the focus on the OS or the type of device versus the function. The world market for computing function is still growing, and most of that growth is not happening on Windows or Mac OS. Most of the function growth and a lot of the existing computing functions is coming to or moving to other platforms that are powered by the Linux kernel and cloud servers. For example, my son's school just handed out Chromebooks to all the kids the other day, because the vast majority of classroom computing function can be done on Chrome OS / Google classroom.
Most of my computing function can be done on my Android phone or Amazon Fire HDX tablet because I use software that allows me to work from multiple devices (Evernote for example). I still use my 7-year-old Macbook as my main work computer, but it no longer travels with me because I don't need it to do most things. When I do need it from a distance, I can simply Remote Desktop into it.
My house with 6 people has about 20 internet connected devices and one uses Windows and the other uses Mac OS. My 4 kids almost never use a Windows or Mac OS, and yet they use computing devices all the time. They use Amazon Fires, an iPod, Android phones, an Amazon Echo, a PS3, a Chromecast, a Chromebox (hooked to my TV), and a couple of older laptops resurrected with Linux distros on them. Even on the old laptops, the functionality they use is almost exclusively web based so they don't really even need the full Linux OS for that either.
I as the IT guy of the family and my wife as the business manager still need to use some of the functionality of the full OS (we use Quicken for finances), but even for us, 90% of what we do could be done on multiple platforms.
In the very near future, the point will not be the OS, but the functionality. Hardware and operating systems will need to be able to handle the functions we want to do.
It does not matter that most phones are disposable after a year, because the work product remains and a simple log into your accounts repopulates your new phone with all your old data and functions, plus whatever new things the new phone can do. Even the corporate model is going the way of taking the computing function to the cloud, making devices and OS's simply workstations rather than servers.
Therefore the whole OS argument is quickly becoming moot as we move to function and cloud-driven computing.