The next versions of iOS and OS X are supposed to focus on performance and stability instead of new features, and that focus on performance could extend all the way back to devices that Apple released three and four years ago. According to 9to5Mac, a focus of iOS 9 has been optimizing the OS for old devices, including the iPhone 4S and iPad mini, neither of which handles iOS 8 very well. That'd be a change for Apple, which typically drops support for devices once they get that old. Apple is reported to have built a "core version" of iOS 9 that's designed for these older devices. They will reportedly run that instead of receiving the OS as it's optimized for Apple's newest hardware.
The iPhone 4S and iPad mini could be in better shape than they are now
That would be an important change for iOS. Apple has increasingly been encouraging people to buy older phones, like the widely advertised iPhone 5C, and this should help those devices stay in good shape. If the newest versions of iOS don't run smoothly on the 5C — which is certainly a risk — people are going to have a worse time with the phone and be less likely to buy from Apple again. That could help Apple in emerging markets, where in the past it's kept old devices around for longer. It's also meaningful for anyone who buys an iPad mini. They're still on sale, even though they aren't doing too well on performance.
Update: Read the Apple iOS 9 review.
In a wide-ranging article on the changes coming to iOS and OS X this year, 9to5Mac reports on a number of other possible new features. For the most part, those focus on security. The major addition is reported to be a feature called "Rootless," which is meant to defend from malware and keep data safe by preventing access to important parts of an OS. The feature can reportedly be disabled on OS X but not on iOS. The change is also supposed to make it much harder to jailbreak an iPhone or iPad. Additional security features are reported to include transitioning more apps over to iCloud Drive, which should enhance their encryption, and using better encryption when on an unfamiliar Wi-Fi network.
As for OS X, 9to5Mac reports that it could receive an iOS-like Control Center that offers quick access to frequently used controls. Other than that, feature additions are supposed to be limited, with the focus on stability and continuing to retouch the interface. Apple should begin detailing what's coming this year at an event next month, on June 8th, so it won't be long until we learn a lot more about its plans.
Verge Video: This is the best keyboard for your iPad