I have considered this, however, this also allows me to have more finite control over it. I also want this to be completely independent of the OS so I can feel free to use whatever OS I want to and recreate the project for my other PCs. This will eventually be expanded to function on a headless litecoin mining rig I am working on with a friend. Also, at least in Windows and the Linux distros I use all include an option for what to do when the power button is pressed. This would let me mimic a button press to initiate the standard shutdown if the temperature reaches a certain point. If the PC fails to shutdown after a certain amount of time and the temperature continues to rise, that is the point that I will have it effectively "press and hold" the power to hard shutdown.
This is, in many ways, intended to be overly engineered just to ensure that my precious PC doesn't get damaged.