Machine learning has been used in games for decades. It has a few applications that make it viable.
Genetic algorithm's are used a lot and I suppose are a form of machine learning.
Voice recognition has been tried in games, I think the last one was "Tom Clancy's Total War" or something like that.
Never works very well
Innovation is a word much misused in games. I cannot count the number of times you read a press release that says something like "\ features an innovative \ never seen in games before" and when you actually look at it you find that all they have done is change the attack button from "A" to "X" or something else as trivial.
We do need innovation, but we aren't going to get it through the major companies. The risk involved for them is just too great.
So it's down to the indies to come up with the next big thing.