A page on the Steam site says that the “Steam universe is expanding” and provides this tiny hint at what we’ll actually see:
Steam is bringing the best games and user-generated content to exciting new destinations. At GDC 2015, we’ll be giving demos of the refined Steam Controller, new living room devices, and a previously-unannounced SteamVR hardware system.
With the introduction of SteamVR hardware, Valve is actively seeking VR content creators. Are you a developer or publisher interested in experiencing the new SteamVR hardware? We’ll be giving scheduled VR demos during the week of GDC, March 4th-6th, 2015, at Moscone Center in San Francisco.
It’s unclear exactly what the company is working on, but it sounds like it’ll be some sort of headset for virtual reality experiences, like the Oculus Rift.
We’ll know more within a week!