If gaben seriously thinks any but the most hardcore will move to linux hes on some serious shit. If this is just something for hardcore pc gamers to have a sort of separate gaming pc in their living room, I see it doing as well as all the other attempts to control the living room from tech companies.
I'm more interested in the idea I see on non gaming sites that thinks valve sees the pc is dying which will eventually lead to a decline in pc gaming as more and more just buy tablets. If this turns out to be essentially a competitor to the mainstream consoles with set specs that developers can create games in mind for we might have something interesting. If this steambox can run ps4 and xbone pc ports for 500 or less I might even buy the thing