Tim on Size Classes
Tim Schmitz, Reading the Size Class Tea Leaves:
Both the iPad Air and the iPad mini have a “regular” size class in both dimensions, which implies that Apple is at least leaving room for something larger than the iPad. The likeliest explanation is that they’re keeping their options open for shipping larger devices in the future. Maybe a larger “iPad Pro?” Or perhaps an Apple TV SDK, in which the TV has a “large” size class.