One thing I was wondering if would be built into iOS7 was the ability to scale to different resolutions. The absence of this feature means that Apple has limited options in selecting screen resolutions for it iDevices. Basically, when bumping up resolution Apple has two choices. On is to "double" resolution (actually, quadruple the number of pixels) like it did when it moved from the iPhone 3GS to the iPhone 4, which when from 320 x 480 to 640 x 960, or the iPad which moved from 1024 x 768 to 1536 x 2048. The second option is to add a row, like it did when it went with a longer display, basically adding a 640 x 176 row over the current 640 x 960 display of the iPhone 4 and 4S.
No mention of the ability to scale to different resolutions was made when Apple unveiled iOS7. If iOS was able to scale to different resolutions, the 640 x 1136 display could migrate to a rather impressive 4-inch HD 720 x 1280 display. But this is not in iOS' bag of tricks.
This means that the next logical step up for the iPhone resolution would be to move up to 1280 x 2272. Now that is an impressive feature and would be Apple's first HD and Full HD display for a smartphone. But it really makes little sense to put a 1280 x 2272 display on a 4-inch screen.
In all likelihood, when Apple launches its iPhone 5S later this year it would still retain the same 640 x 1136 display, which really is sharp enough for a 4-inch display. Still, this means it looses it retina marketing tool. It is a bit hard to talk up a sharp display, when you have a 326 pixel per inch (ppi) display, while Windows Phone have 342 ppi displays, BlackBerry phones hit 355 ppi and Android phones offer staggering 469 ppi.
Basically, as new Windows, BlackBerry and Android models comes out, whatever Apple does with does with its iPhone 5, it will start to look more and more like mid-level offerings from its competitors.
Now Apple has been reportedly looking at manufacturing larger 4.7 and 5.7-inch iPhones. This is really inevitable. I have no doubt Apple can source a 1280 x 2272 display from one of its suppliers. But without a bigger phone, it really won't have a platform to show off this new technology.