Comment 8 for bug 1570310

@pitti, This is probably not useful, since I just ran aptitude as soon as the upgrade to 16 completed with errors, and had it fix the broken packages (with no problems). So systemd seems to be installed fine for me too, now. Just in case there is some clue, though, here is the current output from the two debug commands you mentioned:

steven@goliath:~$ sudo sed -i '2 s/^.*/set -x/' /var/lib/dpkg/info/systemd.prerm
steven@goliath:~$ sudo apt-get install --reinstall systemd
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
Need to get 0 B/3,643 kB of archives.
After this operation, 0 B of additional disk space will be used.
(Reading database ... 186822 files and directories currently installed.)
Preparing to unpack .../systemd_229-4ubuntu4_amd64.deb ...
+ set -e
+ [ upgrade = remove ]
+ dpkg-maintscript-helper rm_conffile /etc/X11/xinit/xinitrc.d/50-systemd-user.sh 228-3~ -- upgrade 229-4ubuntu4
+ dpkg-maintscript-helper rm_conffile /etc/dbus-1/system.d/org.freedesktop.machine1.conf 228-5~ -- upgrade 229-4ubuntu4
+ dpkg-maintscript-helper mv_conffile /etc/systemd/systemd-journald.conf /etc/systemd/journald.conf 204-1~ -- upgrade 229-4ubuntu4
+ dpkg-maintscript-helper mv_conffile /etc/systemd/systemd-logind.conf /etc/systemd/logind.conf 204-1~ -- upgrade 229-4ubuntu4
+ dpkg-maintscript-helper rm_conffile /etc/bash_completion.d/systemd-bash-completion.sh 204-1~ -- upgrade 229-4ubuntu4
+ dpkg-maintscript-helper rm_conffile /etc/bash_completion.d/systemctl-bash-completion.sh 204-1~ -- upgrade 229-4ubuntu4
Unpacking systemd (229-4ubuntu4) over (229-4ubuntu4) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for dbus (1.10.6-1ubuntu3) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up systemd (229-4ubuntu4) ...
addgroup: The group `systemd-journal' already exists as a system group. Exiting.
steven@goliath:~$