I think the future of Google Glass is paring it up with tech like what Emotiv has been working on (http://www.emotiv.com/epoc/features.php). It's already on your head and if we can get the Emotiv like tech far enough to understand a few distinct commands it would create some amazing synergy. If it can recognize my when I think "back" or "home" and maybe "up" and "down" for cycling through menus we can save voice for command sequences.
So if you get a message notification on-screen you can read it and just think "back." Glass would interpret it as a swipe up on the touch or saying "back" by voice, and the message will be marked as read and the screen will turn off. I think voice commands are still very useful for what would be sequences like "Give me directions to the nearest Dunkin Donuts."