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.

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

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.