The most recent thing I've read about the phoenetic library of Majel's voice is from this interview last month with Rod Roddenberry:
When we talked to Google, we were missing a few elements of the phonetic sound of her voice. At the time, they suggested a voice artist come in and finish the sounds, and I felt that wasn’t authentic enough. Now, I’ve been told there is the technology that can take a sample of all this and then fill in those gaps pretty organically or make it sound organic. I think it’ll happen one day.