I'm with Finn, I would like to see more width. I have big hands and have a terrible time typing on the 5 since it is so narrow. I feel it is more than screen size though, you need to look at the overall ergonomics. I briefly owned a HTC Droid DNA with the 5" screen. I didn't think too much about the one handed use argument until I had the DNA. I walked in to a Verizon store and saw the DNA for the first time and it's gorgeous 5" LCD screen and was totally wowed by it. I ended up picking up a used DNA to take for a test run and after using it for only a few days I found it somewhat cumbersome to use with one hand and didn't care for it. I also thought I liked Android playing with it in the store, but didn't care for it after really using it. I have a z10 and it is great for one handed use. I recently played with a Moto X, it is the same height and width as the z10 and I find them to be about perfect. I played with a HTC One and thought it was better than the DNA and really nice until I handled the Moto X. The z10 could easily have a 4.5" screen if it didn't have the ridiculously large bezel. I would like to see the iPhone sized the same as the z10 and the Moto X and then work backwards from there by fitting the largest screen in to it that they could by minimizing the bezel on the top and the sides and keeping the minimum space needed for the home button. Also whatever they do, I hope I never see a AMOLED screen in an any iPhone, I think the Retina display beats any AMOLED display on any phone by any manufacturer.
The z10 and the Nokia Lumia 920 also have a shorter and wider aspect ratio than the 16:9 aspect ratio of the iPhone 5 and most other phones now. The Lumia's 4.5" screen with it's wider aspect ratio would fit in the z10 body, would leave enough room for the home button, and would give a nice amount of added width without having a real tall display.
The software could also be tweaked so that things like going backwards in email, or the address bar in Safari were moved to the bottom of the screen like they are in BB10. If your not reaching for the top corner of the screen, you wouldn't notice the bigger size near as much.
I don't plan on buying a new iPhone until there is one with a larger display. I might pick up another used 5 though since I'm not sure how long I will put up with the quirkiness of the z10.
If and when Apple does offer an iPhone with a larger display, I am sure it will be like stepping up from the 3 series BMW that the iPhone is now to a 5 series.