That’s always been their plan, but it’s getting hit with Valve Time. My guess is that they won’t do it until all issues the major with NVIDIA GPUs have been fixed, as a public build that doesn’t run properly on a majority of machines wouldn’t go well. The latest driver is pretty good, but the Big Picture mode is still pretty much unusable.

At the very least they’re currently trying to bring official support over to other handhelds, as they’ve already confirmed support for the ROG Ally and pushed out a update to SteamOS for the controller support.