Valve employee alfred just confirmed that the Linux port of Steam will support Big Picture.
alfred: “Steam on Linux will fully support Big Picture mode and it should be available right around the full public release.”
About: Heading to the living room—or anywhere there’s a big screen—is Steam’s soon-to-be-released big-picture mode, offering simple, easy-to-read navigation designed specifically for TV. With full controller support, big-picture mode will let gamers kick back and enjoy their favorite games on the biggest screen in the house.
Steam’s big-picture mode doesn’t require any additional development from you. Just ensure your game works well with a controller, and we’ll take care of the rest. And don’t worry, keyboard and mouse aren’t going anywhere—users will be able to switch between input devices at any time.