You know the WWDC tagline says: Epicenter Of Change. Maybe it's related to the core of iOS and OS X like RAM, memory, performance? Because they're logically the epicenter of every OSs.
Maybe Apple is changing the way iOS works? To improve it in terms of RAM, performance like Google did with Lollipop. Lollipop could run on 512MB RAM very smoothly, have improved the battery of Nexus through a OS upgrade. Maybe Apple will do the same too and make it possible to run iOS 9 on 4S better than iOS 8? And very much improved and enhanced on newer devices.
Maybe Apple is changing the way iOS works? To improve it in terms of RAM, performance like Google did with Lollipop. Lollipop could run on 512MB RAM very smoothly, have improved the battery of Nexus through a OS upgrade. Maybe Apple will do the same too and make it possible to run iOS 9 on 4S better than iOS 8? And very much improved and enhanced on newer devices.