It's working for me with my Xbone controller! PS4 controller does nothing yet.
This is an ongoing thing from what I could understand. They'll probably keep updating it like the rest of their gamepad API's but mostly on the side without any major announcements (probably when they start focusing on VR controller support again).
If you or anyone else reading this would like to release a game on Steam, just use the "Partial Controller Support" tag to be on the safe side of things. It's always a slippery slope with gamepad support on the Web.