I predict that air gestures will spread not as a replacement for existing interaction methods, but as an alternative for achieving specific purposes.
I agree with this statement. Although watching Tony Stark work with Jarvis to manipulate incredibly complex machines on his computer using air gestures is visually incredible, I do not see see air gestures "taking off" due to it being largely incompatible with people who may have issues with motor skills, or users in a limited space such as airports or public transportation.