It sort of makes sense. Systemd has many utilities which can replace stuff from Busybox. And Busybox contains its own init system.
Also, most of systems using busybox shouldn't be running Systemd (or any other 'new' init system to be honest)
I will use the Linux kernel (although it is not my favorite kernel).
But I am interested very little in GNU userlands and all the idiosyncracies, complexity and politics that comes with them.