There's also technically a "parallel universe" where IBM picked their inhouse IBM 801 RISC processor and accompanying OS for the IBM 5150, and the far reach of x86 never happened. Although the far reach of the PC wouldn't have either, as the reason that happened is because PCs became easy to clone, and Microsoft had the rights to supply MS-DOS to competitors of IBM. With an in-house IBM chip, that'd have never happened. Who knows what computer line would have become the dominant force? Or maybe the market would be more fragmented, like it was in the 80s computer boom?
Working backwards, I've always assumed that the ultimate evolution of the home computer will be a screen that connects to the internet, essentially the network computer concept that was so beloved of Larry Ellison in the late 1990s. It would either stream games or have enough local processing power to run games, but the big debate won't so much be between different operating systems as between slightly different graphics APIs. The operating system will be as obscure to the man and woman in the street as the operating system of the typical smart television is nowadays.
People will of course still need to render video, but that strikes me as something ideally suited to off-site server farms, in which case the big problem is fast, secure data transfer rather than local processing power - a network engineering problem. The remote servers will of course need an operating system, but that won't be something the average user needs to worry about.
Of course that kind of thing is years away. It may well be that there is an upper limit to the amount of data that can be transmitted from one part of the world to another. The speed of light will always be a problem, although speculative pipelining might be able to ameliorate that.
The internet was really the killer app for home computers, the thing that made them ubiquitous. For millions of new computer owners in the 1990s the local operating system was just a means of getting on the internet. According to these figures more PCs were sold in 1996 than from 1981-1991, and the number has only increased since then.:
In fact judging by those figures more home computers of any kind were sold from 2000-2004 than from 1975-1999, so from a historical perspective - from the perspective of someone looking back from the year 2100 - the evolution of MacOS and OSX and Windows and CP/M, CYCLADES and XANADU etc, and all the untaken paths etc, they are just a small historical curiosity.
They were all just means to an end. Methods by which the great mass of humanity could watch a 23-year-old multimillionaire pretend to be surprised by a new weapon in
Fortnite, in 4K, at 120fps. Think of all the billions of people who died before
Fortnite streaming was a thing. They never knew what we would become.