A patent dating back to 2009 shows Valve has been cooking up a controller like the one mentioned in connection with its rumoured Steam Box.
The patent shows a control pad in which the buttons and analog sticks can be swapped out with unusual inputs like trackpads. The control pad automatically detects and adjusts its input-output for new components. It wads filed in 2009 and published in 2011.
Rumours about Valve's foray into hardware manufacturing broke over the weekend, and made specific reference to just such a controller. Details of a micro PC developed by Valve's Greg Coomer have been tentatively linked with the project.