Gabe definitely mentioned at one point that there was a possibility of putting some basic biometric hardware into a controller, and they've also spoken about experimenting with new forms of input before (and have supported 3rd party novel input devices such as the Novint Falcon).
It's very clear they want to experiment in the controller space, and they have stated multiple times that they do not want to be in the console business, and would rather provide the software for other companies to build their own "Steam Boxes" - yet for some reason everyone fixates on the baseless rumour that they will be making a console, rather than the play that's right in front of them.
It's either that or they are predicting a sharp upsurge in Linux usage after Windows 8 which seems like a very scary predication to make.
Assuming such a steambox does exist, what remains to be seen is whether they make it easy to turn it into a proper Linux PC.
That would effectively stealth install Linux desktops in millions of homes worldwide.