SteamOS is "just" a linux environment optimized for steam. If you install Steam on Ubuntu you have pretty much the same "Steam OS". If you are talking about making a "SteamOS" game, it insinuates integrating the steamworks API that works just as well on any steam client on any platform. It not something new.
What you people are asking for is Linux compatibility. Swen told in the latest Q&A that they are working on this.
