In addition to the SteamOS that will be arriving, there will be Steam machines that will be arriving next year. They will be low-end, mid-end and high-end machines so take your pick on which one do you want for Steam gaming. Of course, the OS itself is Linux based ever since the former Microsoft employee working at Value had taken Windows 8 for a major product disaster.
But first, those machines are still in development and you can participate in hardware beta-testing. You have until October 25th before the list will be locked according to the official website.
Until then, we may have to know what kind of Linux OS Steam OS will be using and besides, we have to wait until the OS itself is out. Will this be a new opportunity for me to try out on my existing computer as there are way too many Linux distributions to choose from?