This is super neat even though it's basically just running the main board plugged into peripherals - I already knew the main board was pretty small but it's still surprising seeing it sitting on a table.
Makes me wonder what you could do with a case the size of a wii (or even a mini wii). Plenty of space for cooling, a 2.5" SSD bay, and I'm sure you could fit lots of other goodies in it too.
You'll probably have to wait a while! They made a statement earlier in the year about wanting to release SteamOS3 just for handhelds rather than every PC, so I get the impression that they want to try and perfect one thing before expanding, rather than trying to rush out a load of ideas before they're ready.