Too late now but it turns out that maybe, just maybe, I did not need to factory reset after all.

Having done the reset and updates back to Jämsänjoki, I encountered the BSOD again on the next reboot. It turns out that the damn thing does not boot if my TOHOLED is on. When I put it on after the reboot, it works fine.

So maybe the first BSOD after the update was due to the same problem.