Re: No halt/poweroff on an EliteBook 840 G1 after upgrade
> Could you please point me (us?) to a good and reasonably short summary
> about the known issues in debian related to systemd, and how to switch
> back to sysvinit, in case?
There is no real switch back. Systemd grabbed libpam (login) which now is libpam-systemd, and is required by policy-kit, networkmanager, gdm, and finally just Gnome session, and also is required by udisks2 which k3b needs ... and so forth. You'll find something everywhere which finally pulls in systemd. So it will be installed anyway.
But you can revert to the sysv init system (reading the rc files) by installing systemd-shim and sysvinit packages, and add kernel commandline 'init=/lib/sysvinit/init' (probably best in a separate menu entry added to /etc/grub.d/custom.cfg).
At least this is how i understood things and it works for me.
If your problem is just only hardware issues then this is probably overkill and you should just try to track it down and file a bug.