I noticed that the image caption of the Steam Machine here in the article could use a correction. It's USB-A, USB-A, microSD. There's no USB-c on the front, but one at the back.
4k60 over oculink is likely going to be difficult for any game. I'm not certain which PCI-E version it's using but an internal GPU will have 2x or 4x the bandwidth via at least an 8x PCI-E 4.0 connection.
Not a single Valve game tested is a travesty, as those would easily hit 4k and over 60fps 😄
A popular YouTube channel has attempted to recreate the Steam Machine's expected behaviour by building a compact PC configured to mimic Valve's leaked CPU, GPU and power limits. Their goal is to test claims such as 4K 60 FPS gaming and higher-end emulation support.