Tell me, have you actually used systemd? Because you're completely misunderstanding the first two points as they're overtly not the case. Particularly the first point, as what it is saying is that they are willing to use newish features in the kernel, not that you are forced to always be running the latest bleeding edge kernel to have an up to date systemd.

The second point has some validity, but is a distortion. Of course you couldn't plug ConsoleKit in as a replacement for logind, because ConsoleKit was never designed for that. What you can do with logind is implement a simple compatibility layer with the standard systemd interfaces and then use it; this is what Ubuntu is doing. What is mandatory to use systemd's services is to implement its protocol for communicating between the services. This is why some of the services are "core" ones- because they're implementing the basic functionality common to the other modules. They can still be replaced, as long as the replacement obeys the same interfaces. This is however a problem for BSD, as the easiest way to use the systemd components is to implement the interface, but that does require features that are only present on Linux.

> By that definition nothing is ever required.

And yes, that was exactly my point. The term "GNU/Linux" is meaningless and doesn't require anything specific. What you might want out of a GNU/Linux system is probably totally different than what I do. You might want Emacs, but I'm a Vi guy. I don't want Emacs and you might not want Vi. How do we settle this? Committee vote? Mud wrestling?