After Steam Bigbox, or whatever it is called, I fail to see the point of this. Isn't it simpler too hook your TV into your home network and access you proper Steam via the controller.
For the same reason why Steamwork usage is free; to get rid of their competitors or at least to have an edge over them. IF it works not only most games will be using Steamwork and be tied to Steam, but also there will be a "controlled" hardware, controlled by Valve, with "probably" a custom controlled OS on which they can do nearly anything for which the game could be optimized. In the end Valve would control the DRM, the distribution method and the hardware/os...
If anything, IF it works (i.e. become popular) I don't see anything good coming out of it, not only it will increase Valve hegemony on "PC" gaming but there is also a risk of having PC games optimized/patched for this "steambox" without much care for the others PC configuration, not to mention the risk of having some games exclusive for Steambox and not working on a standard PC.