Installed, got expected errors, did a hard reset.
On the first reboot after the hard reset, the system didn't give me output on my monitors even though I waited a fair while (gtx 970, 44x.xx driver). It was responsive in the sense that I could ctrl+alt+del it 6 times and have systemd initiate a reboot.
On the 2nd reboot after the hard reset, I temporarily removed 'quiet' and 'splash' from the kernel command line parameters and set systemd to show messages on boot. This time the system booted as expected to SDDM.
When I looked in the journal, I could see that the system was on its way up during the 1st boot (it went as far as activating the network at least), so no idea why it failed to activate my monitor. The journal shows I waited for around a minute for the monitor come alive before deciding to reboot (the services were torn down nicely).
Summa summarum: Update worked, I encountered an unspecified local issue which I can't reproduce, and I recovered simply by doing the quick ctrl+alt+delete x6 dance which systemd caught as expected.
