Steam Box is a device aimed at a PC gaming audience (also known as Master Race) who are, in general, fairly saavy when it comes to technology. The people with a large steam library that would benefit from this are also the people who probably build their own machines. When you slap together some mid-tier architecture that can't even play current gen games at max specs, and the pricepoint is 500 to get your foot in the door? Yeah, the people with existing steam libraries are just going to continue to game with their PC, or build a rig for the same price but better specs to do exactly what the steam box is doing. I get the idea that it's a no-knowledge "console" to run -some- steam games from, but really how many people out there are using steam, would want that functionality, and don't understand how to put together a modern PC? Or, even more likely, wouldn't just google/youtube up information and tips on building their own "Steambox" from newegg/amazon for less? The Linux problem is immediately apparent, and it would be like releasing the Mac OS version of this and infuriating the shit out of most people because the Mac steam library is paltry compared to PC.
I just can't see this being that big of a seller, especially when you can't even play a ton of popular games due to them not being written for linux. I just don't really get what audience this was aimed at in the first place.