Doesn't necessarily have to be, but I think this kind of application for it would be fairly nice. It'd let the whole thing look unobtrusive and if done correctly could be a very easy way to do it for people who have little to no other control over themselves (ALS is in my mind mostly).
The article cites a Google patent[1] for eye tracking within a wearable computing device. Hopefully it's still coming down the pipeline for Glass at some point.
