I've restored the / partition from backup and I've retried: the messages from dracut shows that the move is done cleanly, sysctl still gives error when trying to start /var/tmp
Dependency failed. Aborted start of Setup links in /... running kernel [ABORT]
Dependency failed. Aborted start of Mark the need to...el after reboot [ABORT]
Dependency failed. Aborted start of Relabel all file...s, if necessary [ABORT]
$ systemctl status var-tmp.mount:
Failed to get D-Bus connection: Failed to connect to socket /run/systemd/private: No such file or directory
$ ls -la /run shows the existence of only one directory inside: /run/udev/
dmesg shows multiple lines containing:
systemd-cgroups-agent[PID]: Failed to get D-Bus connection: Failed to connect to socket /org/freedesktop/systemd1/private: Connection refused
same message after rebooting with the standard kernel
starting dbus-launcher by hand, followed by /bin/systemd creates the directory /run/systemd, but there is no socket inside, just 2 empty subdirs "ask-password" and "system"
Why, oh why, I get the impression that I'm going towards a fresh installation of Mageia 3?

Edit: preparing my bugreport...