I don't think that we can safely say that "this is not a firmware problem", as the "this" doesn't appear to be the same thing for all people.
I'm beginning to suspect that this update is triggering a number ill effects that may be due to errors in the SMC, errors in the updating process, interactions with unaccounted for conditions or computer states, or from secondary effects caused by a combination of the above.
I know that my internal video problems are not based on the os. The machine will boot and work on an external display, no matter which disk or OS version I boot from.
The machine will NOT boot and keep the display working for more than a few seconds when using ONLY the internal display no matter which disk or OS I boot from.
It's almost like the machine is stuck in some weird sudo-clamshell mode, even when there is no external display connected or USB device attached.
It may be that some non-PRAM stored setting got corrupted that controls the video sleep subsystem, or the system that determines whether the lid is closed, etc... My machine was running in dual monitor mode with a mouse attached when the update was applied- perhaps that and some other condition triggered some unforeseen bug, or exacerbated an existing issue...
Or it may be that something about the update process or SMC firmware caused the well known nVidea video hardware bug to manifest by allowing something in the nVideo card to momentarily overheat.
It could be these or a lot of things, or possibly some other issue that just happened to rear it's head at the exact moment the computer rebooted after applying the SMC update.
I have an appointment Thursday at the genius bar- until then I'm on external display mode only. I'll let you all know if I find out anything new...