What about initrd? Most of those use busybox and it's now "recommended" to start systemd there. (Granted, I don't see why anyone would run busybox's syslog - the only component affected by this change - in an initrd.)
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.