It's not compatability that's the problem. Apparently the firmware flash doesn't have checksums or check itself. If it's corrupt, it just goes ahead anyway. It also doesn't check to see if you password protected the firmware, so it will fail on that, too.
Inexcusably stupid. Firmware updates should always be standalone and with a backup power supply, and then only to fix a major bug. People set auto updates, trusting Apple.
I don't understand why video driver updates require a firmware update. That's apparently what started all this.
Worker, there were reports of kernel panics with this. If the video driver update was corrupt, then the boot fails.