I dislike the idea of having a steam console.
I think consoles generally limit the graphical capabilities of the actual games themselves, and then valve will have to make games that are limited by their own consoles processing power. Which pretty much means, valve will stop making games for the highest end of computers. Though, truth be told, they don't do that much anyway. Also, Valve has kind of always been about allowing gamers to modify their games, A console could limit that. Also, one last thing, is that it's harder to social network on a console.
I'm not exactly keen on a steam console xD