If you do run into cases where something doesn't work as expected with sysvinit instead of systemd, please do file a bug.

For that matter, if this is a use case you care about, systemd-shim could use a maintainer or maintenance team: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=832508

Yes, it's true.

To replace PID 1 with sysvinit, run:

  apt-get install sysvinit-core systemd-sysv-
  reboot

To prevent it from coming back, create the file /etc/apt/preferences.d/no-systemd.pref containing:

  Package: systemd-sysv
  Pin: origin *
  Pin-Priority: -1

This works great on servers and lightweight desktops. As others have noted, if you want GNOME you also need to install systemd-shim. I have no experience with this, but I have no reason to doubt that it works.

I'm running openRC on all my systems and the problem is usually dependencies. As an example, both Brasero and K3b depends on something that depends on systemd. I can understand if a program uses the systemd library but these need systemd as pid 1 because reasons.