> Also, different boot systems can be made compatible and exchanged at will. Debian does (and should always) support a few of them.
I strongly disagree. Supporting multiple init systems leads to a pointless increase in complexity, which leads to more work and makes testing harder. Nobody wants three init systems that all sort of work, people just want one that works really well. Debian should pick a single init system, and it's obviously systemd given its technical superiority over all its contenders. kFreeBSD must obviously use sysvinit, as neither systemd nor upstart run on the FreeBSD kernel, but it should be used only on kFreeBSD. That way, eventual sysvinit breakage will be confined to users of that OS.