My wager would be AR. We have a few years yet before we see useful, comfortable, well-designed AR environments, but once they cross a certain threshold they'll

My wager would be AR. We have a few years yet before we see useful, comfortable, well-designed AR environments, but once they cross a certain threshold they'll immediately obsolete a massive section of the computer dislay market, as well as provide numerous opportunities for further innovation. Given that it's a market in which products will succeed or fail based primarily on UX, ease of use, and quality of design, each a strong point of Apple, they have the potential to take the sector by storm.