I think that Valve is more looking at peripherals as opposed to a whole system.
I'm pretty sure Valve is wanting to help look forward to devices like the Razer Hydra. It was supposed to have been a big step forward in controlling games, similar to the Wii but with much better accuracy. Problem was, it didn't work nearly as well as it was supposed to and I don't think Razer is bothering to improve it now since it didn't sell well. When it came out (and still is), it was sold with a copy of Portal 2 that had 6 levels designed by Valve for use with this device. This tells me that Valve wanted it to a success. It just didn't and now Valve is going to try to do it themselves.
While many of us have seen the Valve controller (it was linked here by nin), I don't think that is the only idea Valve is playing with and the Hydra being the proof of that I feel.
*automatically refuses to place horse heads in anyone's bed*