"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
iPad Mini 4 Uses Speed-Bumped 1.5 GHz A8 Chip With 2 GB of RAM
Having a whole extra CPU core makes the 1.5GHz A8X in the iPad Air 2 about 50% faster than the Mini 4, but we're still looking at a 20-or-so percent improvement over the old Mini 2 and Mini 3. That extra RAM will be good for more than just Split View multitasking, too—2GB iDevices need to eject things from memory less often, cutting down on the amount of tab reloading that Safari does and generally reducing wait times when switching between different tabs and apps.With the iPad mini 4 using a slower chip than the iPad Air 2 while still driving the same display resolution and similar other internals, performance won't be quite as good on the smaller tablet, as the smaller body likely has some heat-related impacts that drove Apple to include the less-powerful chip. Still, users should see substantial performance upgrades over earlier iPad mini models, as well as support for all of the latest iOS 9 features like Split View multitasking.