This is already happening, I think. I found a "bug" in quicktime like two months ago, no one listened on the rumor forums, maybe i'm a jackass. Find a macbook, or mbp. Open quicktime to watch a movie. Hold down one finger. Move the other one side to side. You are controlling volume at this point. I don't think it will be more then the base of the keyboard, but multi touch is coming, I think quicktime was the leak. What the implementation looks like, i don't know. I'd like to see the whole bottom of the keyboad turn into a trackpad, two hands on screen at once, like different dots or something for reference. Or, they can build it into the display, but I think the mouse will soon be dead, no matter what. Hopefully we can find a way to play doom.
Multi-Touch Coming to a Mac Near You?