A new report by The Verge reveals that "the team discovered that hands weren't a good source of biofeedback since they were always moving around." The team ended up experimenting with a lot of prototypes, many of which you can see on Engadget.
So does that mean Valve has abandoned biometric feedback altogether? No. In fact, The Verge claims that the team "hinted" at a future VR headset which "might measure your body's reaction to games at the earlobe." A device like that will be able to know when you're scared or excited, and enabled sweat-based gameplay we didn't know we ever wanted.