This is taken from their website - I dont know what they intended, but it sure looks like a possibility.
In SteamOS, we have achieved significant performance increases in graphics processing, and we’re now targeting audio performance and reductions in input latency at the operating system level.
You could take the statement on the site to seem that they could be working on their own stuff, but if you watch their video it seems that they are keen on working on existing things like SDL and participating in the Khronos group than building things from scratch.
They don't just have "a guy", they have Sam Lantinga, the guy who created SDL. I don't know if he's working on it or not, but the fact that they have him at the company speaks volumes about where they're headed.
