Ok so I figured out what caused my brightness control to disappear, it would seem the latest Intel 4000 drivers (remember this thing has 2 graphics cards - good times huh?) are not compatible with ACPI brightness controls. You do have to update the latest AMD Catalyst drivers, which appear to be the reason why you hit a black / flickering login screen.
I installed the beta driver 13.11
AMD Catalyst? Display Driver
Here's all of the steps for anyone that's reaching the black-screen of death on Chronos 7 Windows 8.1 upgrade:
Restart and HOLD shift-f8 to get into safe mode..
How To Boot Into Safe Mode On Windows 8 (The Easy Way)
Choose Safemode+Network support so you can download the Radeon 13.11 drivers above
Install these while in safe mode, you should be set.
Restart the computer - Windows Login screen should be fine.
Now do a BIOS update if you can - this doesn't seem to work in safemode.
If you've already installed the newest Intel-4000HD drivers, or had to in order to get 8.1 kicking - and want rid of them so brightness controls work this can be done inside "SW Update" from samsung, there's a secret menu of sorts in there:
Lower left corner: "Find Model" - choose NP780 or whatever you have..
click Windows 8
A strange sort of Export tool appears, Uncheck All by using the checkbox at the top
Scroll down and choose "Graphics Driver 64" - this is not AMD driver, don't select that
Next you'll be prompted to save this to your desktop.. the tool will basically download the old HD4000 driver you need. Once on your desktop, browse to the folder and install it. Brightness controls will be restored correctly.