As expected, Apple is always testing new resolutions for their devices. The final, native one is set by iOS and it cannot be changed. Some new files that are part of iOS 8 Beta show the evidence: the next iPhone may have a new resolution.
According to 9to5mac, the files were discovered inside the latest Xcode 6 Software Development Kit (SDK) beta that was seeded to developers. The cited source explains how the files can be found in the iOS 8's Springboard application. The Springboard is the app responsible for showing the home screens.
The mentioned file appears only in the two last versions of Xcode 6 beta and it is optimized for a resolution of 414 by 736 pixels. Hence, the actual retina resolution, which usually doubles the size of the pixels will result in a screen that will have a 828x1472 pixels resolution.
The new resolution is also 16:9, just like the one Apple used for iPhone 5, 5s and 5c. This matches the shape of the leaked screens that we have seen coming from Chinese manufacturers and Apple's supply chain in Asia.
Such a screen becomes retina at 8 inches (20 centimeters) away from your eyes and it should have a density of 422.22 PPI. This matches Apple's self-imposed retina standards. If Apple will use this resolution, they can fit two additional rows and one additional column.
Apple is expected to announce a new iPhone on September 9. The device may come in two different sizes – a 4.7-inch diagonal display and another one with a 5.5-inch screen. The iPhone 6 should be released along with iOS 8. The new operating system for iPhone will not bring major design changes, but will greatly improve the inner workings of iOS 7.
Apple also plans to release OS X Yosemite about the same time. The Mac software and the iPhone one will work together thanks to new features like continuity and handoff. The iPhone user will be able to start an email or browse a page on his iOS device and then, when he moves to his Mac, he can jump exactly in the same document or app, at the point where he left off.