I suspect a Houyhnhnm would reply that the very concept of the requirements changing for a set thing like an "operating system" is a category error- the idea of

I suspect a Houyhnhnm would reply that the very concept of the requirements changing for a set thing like an "operating system" is a category error- the idea of an operating system is defined (by a perfectly rational Houyhnhnm) as a given set of requirements. Change those, and you're now talking about a different kind of thing. We can talk about plenty of things that are (in human-speak) part of the requirements for OSes now that, X years ago, weren't. But (a Houyhnhnm might say) there's an exhaustive set of all things that an OS (qua an OS) should do, and once you have that, you have an OS that will stand the test of time (essentially) unchanged. We hadn't (and probably still haven't) enumerated and implemented all of these capabilities simply because our primitive computing technology base is still coming of age. Really, to a computer scientist in 1960, an OS was probably just something that made his mainframe go so that he could do more interesting things. It would take a optimally-rational equine being to sit down at that stage and work out exactly, in an ideal sense applicable to all feasible computing devices, what an OS should be. And its still the case, since I doubt the architects of modern OSes give much thought to quantum computing interfaces or nanite-cloud networking or whatever. But adopting the Houyhnhnm-ist manner of thinking about OSes (or more humble applications) as implementations abstract ideal entities rather than bits of machinery might make it easier when, however long down the road, someone is trying to use our work for something that we hadn't foreseen.