Think of the first slate multi-touch smartphone (the iPhone 1). It started a trend and defined what a smartphone is today, that was, at the time, the "next big thing". It was the introduction of what a smartphone should be, and what we all know it as today. It was something completely new, a computer you could hold in your hands, and perform the everyday simple computer tasks with... and that technology has come a long way and even can serve as a replacement of desktop computers for the general user.
As such, the real "next big thing" to come next, will not be something that is a mere extension of the smartphone, or a new feature. That is miniscule. The "next big thing"... will be something else to completely change and revolutionize everyday life."