Basically just the CPU fan, case, and PSU (if you're lucky). If someone can figure out how to get Doom running on just those 3 things, young people will be able to ascend.
I vaguely remember reading that they have literal ARM cortex chips in some of the most modern case RGB controllers
If we can get to an SPI and connect some kind of display, it's conceivable that we could run DOOM, right?