I am not sure your prediction will come to be. Every year for the last 4 years the tablet market has become more saturated. There are users who prefer Android tablets as well those who prefer IOS. Then there are the users who cannot afford brand new and will instead buy used. Trying to get everyone who already owns a tablet to upgrade to a new one will not be an easy task.
Not to mention there is alot more competition from all over the place now than there was years ago.
In 2011, the iPad 2 was pretty much the only game in town. It was the first tablet for many people, it was a new experience and product for them. iPhones still had 3.5" screens and wasn't a real alternative. In many ways what makes the Air2 so great right now is what made the 2 great when it was released. Thinner, more powerful, more features. They continued to sell this model into 2014.
Nowadays people are already sitting on a tablet and may not see a need to upgrade. If you did want to buy one to replace an iPad 2, they've had 3 years to do so already, and if they waited until now, they have 5 different new iPad models to choose from plus the backlog of used iPads on the market. You have pressure from Android/Amazon tablets in all sorts of sizes and price points. Lets not forget what phablets are doing to the tablet market as well. All this stuff cuts into the potential sales while it was sort of open game before.
Air2 is a great product but I don't think it will be the best selling iPad. Market saturation and competition being the main reasons.