Even gamers nexus' Steve today said that they're about to start doing Linux games performance testing soon. It's happening, y'all, the year of the Linux desktop is upon us. ᕕ(ᐛ)ᕗ
Edit: just wanted to clarify that Steve from GN didn't precisely say they're starting to test soon, he said they will start WHEN the steam OS releases and is adopted. Sorry about that.
From what I recall, it wasn't something you could easily use like a normal distro, and that version was based on Debian (so stable but outdated software). It only worked on some hardware, and you had to do a full system wipe.
More likely, this is them officially partnering with handheld or gaming laptop makers, using their latest Arch-based distro and allowing them to use Valve/Steam branding as a selling point.