Gabe Newell, from Valve software, recently conducted a focus group session with deaf gamers. Three videos are available of this event: Part One, Part Two, and Part Three. Note that the audio quality is, ironically, pretty bad in each video.
One of the most interesting tidbits from these videos involves Valve's desire to introduce a deaf character into a future game (possibly in the Half Life universe). An idea is floated where Alyx has taught Dog sign language, based on a past crush she had with a deaf individual. In essence, it would be an excuse for Valve to develop the necessary technology for characters to sign. Pretty cool.
I think it's great that Valve is doing this. In the accessibility world, blind people get nearly all of the focus. For a gaming company to branch out into this realm is really quite remarkable. I'm looking forward to see how Valve implements this new technology, and I'm excited to see where the Half Life story goes with this (assuming, of course, that Half Life is the intended universe for this work).