Unlike some of the future gaming tech out there audio is one of the sorely neglected yet essential pieces in gaming. Some future items are already out there like various mind control based games with strange devices measuring your alpha and beta brain waves to play a game. What I have in mind though is something a bit more radical. The application of procedural or algorithmic generation to audio and not just graphics. Some basic examples of the idea exist in music using either existing audio that gets slightly adjusted based on variables and conditions or advanced compilations of existing audio based on character actions usually. So far it's been impractical to try and synthesize audio outside the 16 bit range in a game because of size and or practical limitations.
Though now there are some worthy and worth while programs to mention that can generate speech based on text with some less robotic voices. This however is only the beginning. I see a future perhaps one brought by Bethesda and The Elder Scrolls series in which all the audio will be completely generated through code without any actual production audio. Unique music for every dungeon, and dialogue and voices for every NPC. Audio which will be dynamically altered in real time based on various variables. Muffled audio from water or distance in rain, or that ringing and buzz after being too close to an explosion or standing in front of a rock concert speaker for too long. Creating the actual sound of a building collapsing based on what's actually happening in the game. Proper dissipation over distance instead of a flat cutoff at a given distance, and complex audio echo's and bouncing. These details can completely change how we see a world, without them the visuals will be all we really have to rely on and if we're focusing on them more and more it becomes much harder to be immersed when we start noticing out of place polygons or unrealistic movements.
Though of course with some of the strange things I'm seeing in the future of gaming I must say it'll be very interesting to see how they all blend together. With things like the above mentioned controller there's a game designed to estimate if you're on edge or not and then insert random noises, shadows, or enemies to get you back on edge and keep you there. I can only imagine what that will do to the human psyche if someone plays it too long. Forcing you into always being afraid and on edge for hours at a time non stop, imagine meeting that person just after he stops playing. That's one of those lines that while I can appreciate it being crossed I really wouldn't want to do it myself and would have a hard time getting into a game that's profiling me constantly to try and push me into a given emotional state regardless of the final value of it.