OK, sorry, so the problem turned out to be quite trivial after all.
My fstab file contained a line required to support Altera FPGA programmers. It seems that the usbfs "filesystem" is no longer supported at all, causing the error displayed at the top of the first screen-shot.
It looked like the system continues in the boot process happily after the error so I didn't pay attention to it at first. Removing the line however allows the boot to proceed normally.
Still, I find it quite silly that a single unimportant error can cause the whole system to fail to boot, an ordinary PC user would have no idea what to do with it. (I.e. systemd certainly did not make a terribly good first impression on me..)
Thanks, Martin
