SteamBox needs few things to success:
1. Work like console, feel like a console, marketised as a console. If this gonna be just yet another branded PC it won't be anything special and people (Specially console users) won't acknowledge it as Wii U, PS4, Xbox720 (or whatever it will be called) compatition.
2.User base, this is most impotent thing of them all, not just for console but any platform... Linux is one of victims of that. More user = more developer interest.
3.Exlusives deals, show that you have better line up then all other consoles, this is what happens during start of generation.... it what happening now, for example Ninendo got exlusive Beyonetta 2, which was quite a hit on Xbox 360 and PS3. Thru i think without it might go to.
4. Do E3 conference = instant win.... announce Half-life 3 on it early on SteamBox = meltdown, everyone pre-ordering
It's actually good time then ever to make a console since it's generation transition right now