Macerkopf.de reports [Google translation] that it has learned from an Apple software engineer that the company is currently testing fourteen different GPU drivers for iPhone hardware, including several drivers for running displays at higher resolutions of 1280 x 720 and 1440 x 800. The iPhone 4 and 4S currently utilize a 960 x 640 display.
According to the report, Apple is testing two sets of seven drivers each targeting either dual-core or quad-core chips. Within each set, Apple is said to be testing four drivers targeting the current 960 x 640 display size, two targeting 1280 x 720 displays and one targeting 1440 x 800 displays.
The report notes that these drivers are only in testing and thus not necessarily indicative of any shipping product. In addition, the higher resolutions are not clean multiples of the current iPhone resolution, meaning that developers would have to offer newly-scaled content to fit the new size, with Apple having to use a non-ideal automatic scaling to allow current content to display on the new device. In the transition to the current Retina displays, Apple doubled the screen's resolution in both the vertical and horizontal directions, allowing lower-resolution apps to be easily scaled up using pixel doubling techniques.
Macerkopf has not been a frequent source of rumors, and most recently incorrectly claimed that iOS 5.0.2 would be coming in late November to further address battery issues. The claim was later retracted after it was said that memory leaks were delaying the public launch. The original report also cited major enhancements to Siri for the first significant update for iOS 5. But with the first developer build of iOS 5.1 being released last week, there is yet to be any evidence of such Siri enhancements.