Surprisingly, this new KitKat firmware got released first for the GT-I9195 Black Edition and not the regular one and as of now there is only one build available which is meant for the country Belgium, carrier Proximus and for the Black Edition. The build date of the firmware says Fri, 23 May 2014 which means it was under testing for a whole 20 days (let's hope we don't experience any bugs!).
If you wish to try it out, then you may head onto the firmware's download page and download it.
The firmware doesn't have any problems as long as you flash it untouched (aka when you do not delete the KNOX bootloader files). Turns out the issue was not caused by adding a Google account or similar. I have personally tried wiping data, cache, even installing the package again but the phone would still crash and overheat like crazy. Yet when the firmware was flashed untouched (with the KNOX bootloader files), it runs perfectly and hasn't crashed in more than 20 hours now.
This post will be updated once newer builds appear as well as builds for the I9190 and I9192 so be sure to check regularly.