Before you get excited about SpeedRunners listing a Linux/SteamOS build, please keep in mind it's just a test.
When you download the Linux build, it will give you the "Party Mode" demo -- the offline version of SpeedRunners designed for parties and conventions/showcases.
We are testing to see stability of that build, because it has much less dependencies (no online, no multiple controller setups, etc), and once we get the hang of it, we will proceed to port the full version to SteamOS.
Nonetheless a good first step!