Nik Fletcher:

In Session 308 at WWDC, it instantly became clear that this is how Apple believes consumer apps will evolve. Buy or download an app, use the features you bought and over time developers should monetise new features based on the new SDK addition.

IAP is generally hated by most nerd and developer circles, relegated to mass market games like Candy Crush. However, Nik goes down an interesting path to describe a future where app trials and upgrades run through IAP.