They have been talking about doing peripherals for ages now. Gabe has said several times he is interested in using biometric data to detect people's emotions to alter the gameplay. They also have their wearable computing projects etc as well. They even had a build of left for dead that recorded your heart rate and added a metric of how scared you were at the end of each level.
They have flat out said they are not working on a steambox console.
How trivial is this, I mean many of us thought about this back in 2006 when the Wii came out. Probably there hasn't been a business case for it, but some companies believe that some ideas have intrinsic worth and can sell themselves. I'm looking forward to this and am all for it, GO VALVE!
There are so many ideas to make a reality, and we need a big big shaking in the industry real soon.