75% probability of being mainstream, or at least not unusual, by 2020. It seems like the obvious solution: phone screens are too small, laptops and even tablets are too inconvenient to carry around constantly. And I'd go 50/30/20 on the first mass market product being based on Android/Apple/other. (With Android, anybody can build it without asking for permission).
As we did last year, use this thread to make predictions for the next year and next decade, with probabilities attached when practical.
Happy New Year, Less Wrong!