I think you got a bit confused… FEX is used in the steam frame (VR headset) because it uses an ARM processor to save battery. The steam machine uses a normal x64 CPU and appears to be using some relatively standard pc hardware, so no compatibility layers are needed for windows (only drivers are needed) I doubt you’ll be able to install windows on the steam frame though, for the reason you say (arm compatibility is a mess).

The worst is when you get promoted, and people start to recognize you as an expert. At that point you realize how everybody is sort of winging it, including the people in all other professions that you’d really prefer not to (doctors, pilots, politicians …).