There is also no requirement that a Linux distribution includes any GNU software at all, should we refer to them as e.g Busybox/Linux?
I don't agree with this actually, that's why I didn't even mention this. I believe GNU was indispensable to the wider Linux phenomenon. It's a matter of being fair and technically precise.
Alpine Linux (of Docker fame)
Lots of embedded stuff
Not that it invalidates your point, but it has happened.
Alpine Linux (e.g. Docker) and Android
Android shot past all the others to become the most popular operating system in the world, in case you didn't notice.
This is actually what FSF claims to do as far as I understand. GPL is a law hack.
Why do people insist on saying that all of this is one single "operating system" called "GNU/Linux" and that there are different "distros" called Ubuntu, Debian, Fedora, CentOS, Arch, etc., instead of just calling it all a bunch of operating systems? Because these different "distros" are not compatible with each other. They can mostly run each other's binaries, and some configuration knowledge works across them, but other than that they are mostly incompatible. And they are all based on Linux, GNU, and a bunch of non-GNU software.
So if we say that "This is an operating system called Fedora, which is based on Linux and GNU and a bunch of other stuff", instead of "This is a distribution of the operating system GNU/Linux called Fedora" then we would just be better off overall. There is no more reason to fight over the name "GNU/Linux" versus "Linux" since both are pretty inaccurate anyway. There would be no more user confusion about what Linux is, as there seems to be today (e.g. people blame Linux for userland problems, or people expect program X to be packaged and get support for operating system Y because it says "Linux" on the webpage). And things like BSD would seem less foreign if people knew that it's really another operating system instead of being seen as just some weird non-Linux thing.
And if the GNU people ever get around to actually finish their operating system, then they could just call it "GNU" without causing even more confusion