BBC recently got a chance to talk to Gabe Newell about the upcoming Steam Box, Valve's upcoming attempt to bring the Steam platform into the living room. Mr. Newell mentioned that a big hurdle at the moment is deciding on the right type of controller for the system.
One possibility is a controller with sensors in it, in order to "be able to directly measure how aroused the player is - what their heart rate is, things like that - in order to offer them a new experience each time they play." He mentions Left 4 Dead as an example, which could possibly ramp things up considerably if the controller senses that the player is a scaredy-cat.
The article also mentions that Valve is planning to give out prototypes to consumers in order to gauge their reactions to it in "the next three to four months." Regardless of whether or not the Steam Box can tell how aroused I am, consider me on board with the whole idea.