I saw there was an update to my XPS 12 (9Q33, Mid 2013) BIOS about a week ago and decided to install it at some future date. Well today is that future date, and I now regret having done so. As you can see in this picture of the screen (with some minor photoshopping to protect my privacy) it shows 59% programming EC. As I type this, it has been stuck at that point for the last 35 minutes with the fan running very loudly. EDIT: Correction, I just checked and the clock has advanced as has the progress bar, but only to 65% and that's after roughly 40 minutes (difference between that desktop gadget's displayed time, and the system tray time).
I have unplugged the system from power and am now waiting for the battery to die out so that I can determine if my XPS 12 is dead as a brick. Dell, please remove the A07 BIOS update from your site, because as I, and the others who have posted here about this exact same issue have discovered, is clearly a bad update that does bad things to those who install it. I wish I had searched this forum first, and avoided this awful mess.
Now, to the inevitable question regarding my installed video driver version, I don't know what it is, and it may be hours before I know what it is, assuming the laptop works again at all. My best guess is that it is the one currently available on the support page (XPS-9Q33_Video_Driver_1N5FK_WN_10.18.10.3574_A04.EXE), since it appears from my included picture that I downloaded a file on June 27th that is roughly the same size as that file released on May 28.
If the system does boot up, I intend to revert to the A06 BIOS to avoid the issues that others have experienced with A07.
And now the aftermath. Luckily, the system appears to have not suffered any damage and booted into Windows without an issue. I can confirm that the video driver was the 10.18.10.3574 A04 release mentioned above. Windows did produce a system memory dump with a 9f code, which corresponds to a power failure (not surprising since I let the battery drain to regain control of the system). I have also downgraded to the A06 BIOS, and experienced no problems with that process. I sincerely hope that nobody else out there has to go through this.