"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
iOS 9 to Focus Heavily on Stability and Optimization
Sources who spoke to 9to5Mac have suggested that Apple will market iOS 9 similarly to OS X 10.6 Snow Leopard, which was also a maintenance upgrade that resulted in improved performance and better efficiency.
For 2015, iOS 9 is going to include a collection of under-the-hood improvements. Sources tell us that iOS 9 engineers are putting a "huge" focus on fixing bugs, maintaining stability, and boosting performance for the new operating system, rather than solely focusing on delivering major new feature additions. Apple will also continue to make efforts to keep the size of the OS and updates manageable, especially for the many millions of iOS device owners with 16GB devices.An operating system update that aims to optimize performance and fix lingering bugs will likely be welcome news to many iOS 8 users who have been unhappy with the state of the operating system. iOS 8 has suffered from an above average number of bugs since its September introduction, causing issues like slow Wi-Fi, battery drain, screen rotation problems, Bluetooth connectivity failures, and more. The last few minor iOS 8 updates, including 8.1.1, 8.1.2, and 8.1.3 have all been focused on fixing some of these problems.
Apple's goal of reducing the amount of space needed for an operating system update is also welcome news to users who have 16GB devices without much storage space left. iOS 8 has seen slower adoption rates than iOS 7, which many have attributed to its 2GB+ installation size.
Work on iOS 9 is well underway at Apple, and site visits to MacRumors from Apple IP addresses on devices running the new OS have increased over the course of the past month, following the holidays. We first started seeing an uptick in visits from iOS 9 users in December, which declined around Christmas and has picked up once again.
An iOS 9 update that aims for bug fixes and performance improvements won't go entirely without new features -- there are still some rumored enhancements in the works that could be released in the next operating system update, including transit directions and indoor mapping abilities for Maps and split-screen multitasking for iPads. We'll get our first glimpse of iOS 9 at June's Worldwide Developers Conference, but a specific date is still forthcoming.