After coming over from Android, where the ridiculously bigger screens are just becoming way too much, I don't want to see the 5 change. However, I feel the screen could be made larger without the size of the phone increasing, by taking advantage of some of the buffer space near the home key and speaker.
What iPhone really needs to drag Android users over (which, after all, is what Apple's intent should be to increase profits) is to have integrated map and nav like Android offers with Google Maps and their standalone nav interface. If my iPhone could use Siri to locate an address or POI, then I could direct her to navigate me there, allowing Maps to open and offer turn by turn voice directions, this phone would be unbeatable. I hemmed and hawed for a long time before making the switch, but finally did it out of sheer enjoyment for the Apple product quality itself. I still cringe when I am out and about and need to navigate somewhere having to rely on my free apps like Waze to get me there. The maps are usually not current, and the navigation is less than accurate most of the time. I resort to the included map nav, which has no turn by turn voice, which makes it a bit risky to look at and drive.
I'd say this would be a huge selling point. My phone is plenty fast already, and it works flawlessly. I could care less about processors and all that other stuff. Gimme the convenience!