It would be cool
I would love voice software that was built into a game correctly, but I don't think it is going to happen for a lot of reasons.
1. Lack of software that does it in the market today. ViaVoice and Dragonfly were two programs that offered voice-to-text and voice-to-commands options, and they never really took off. Each human voice is unique, and a program needs to be trained on your voice in order to get the commands right. Without that level of training, which involves you sitting there reading chapters from a book at your computer, the quality is never going to be very high.
2. Potential uses that would enhance, not destroy quality of game. Lets be honest, you can say things a lot faster than you can type things. While I think it would be awesome to be sitting there on a RTS game giving voice commands to harvest more gold while managing my army with my mouse, what that means is that an element of the game that would have usually been handled by me will basically be handled by a program, and that takes away a bit of the time-management that a game requires, especially important when it comes to multiplayer.
3. Unfair advantage. If I can issue a ton of commands to shoot the tank or drop a bomb while my character is moving and shooting, I have a huge advantage over someone without voice input. My fear is that developers will put this in place without really thinking it through, and then gamers will appear who create short-hand voice commands for common tasks and events that allow them to never take their hands off of the mouse and wsad keys. It sounds awesome if you are the one doing it, but imagine being a newbie who had no idea whats going on and now everyone is shooting forever without stopping while you fumble to hit the r key as they smoke you.
Just some thoughts.