Many of the lower-end Steam Machines should be capable of doing this, as well as some HTPC implementations (assuming they can run Steam, so not a Roku or AppleTV or such). I'm betting the SteamOS system requirements[1] would be a decent proxy until more information is released, although I doubt that you would require a hard drive that big and a graphics card that powerful.

[1]: http://store.steampowered.com/steamos/buildyourown