Re: Removing conflicts of init system
> sysvinit works similarly, with /lib/sysvinit/init
This was in Jessie, but I don't see any /lib/sysvinit/init in Stretch nor in Sid,
it's /sbin/init now, am I wrong?
You are correct. The sysvinit package (which provided the fallback) was dropped:
* Drop transitional sysvinit package. It has served its purpose for the
wheezy → jessie transition and keeping it around for longer only
leads to confusion as it doesn't setup /etc/inittab which is necessary
to boot with SysV. This functionality has moved into sysvinit-core,
which should be used instead in such a case. (Closes: #781766)
There is nothing blocking its reintroduction, though, if care is taken to make sysvinit functional after installing it.