Designing an OS for Blind/Deaf Users?

Sushant Bhatia asks: "I work for a team developing technology for individuals who are blind and I have had the opportunity to use some screen reading software and while there have been leaps of progress it is still quite tedious to use, and not at all user friendly. One of my managers recently posed an interesting question for me: 'How would you design an OS from scratch that would target individuals who are blind and/or deaf?' What about inputs such as keyboards or refreshable Braille devices?"