According to Dediu’s predictions, he thinks that Apple could hit that mark by the middle of 2017. In addition, he predicts that Apple will have sold at least 1.2 billion units of the iPhone by then, which he then claims helped to spawn a slew of other iOS-powered devices that went on to be successful in their own right, like the iPod Touch, the iPad, and to a certain extent the Apple Watch and Apple TV.
Dediu says that in terms of hardware, we are looking at around $980 billion which is why of the $1 trillion mark, but he expects Apple to make up for the difference through non-hardware sales. This includes revenue generated by apps and in-app subscriptions in which Apple takes a cut of, along with services like iCloud and Apple Music, all of which should push Apple over the $1 trillion mark.
Since this is a prediction it’s hard to say if it will come true. Apple has been struggling on the hardware front since last year with iPhone sales on the decline, although some are expecting Apple to make up for it with this year’s iPhone which analysts have predicted will blow away the sales of the iPhone 6.