I hadn't thought about the possibility that day 3 could be about their VR stuff. Abrash has been beavering away on all that stuff for some time now. It has also been a fair while since he posted anything up on his blog (July 26, 2013): http://blogs.valvesoftware.com/abrash/
2. Steambox
3a. some VR peripheral (looks like a VR goggle/headset to me)
3b. some special cross-play between Steambox and Windows/Mac/Linux
3c. cross play between steambox and PS4