John Gruber thought through the potential new screen sizes Apple would use for the upcoming iPhone 6 lineup. Definitely read his guesswork if you have interest in the subject.
Pixels, points, and inches all accounted for, I still enjoy the size of the iPhone 5s and do not have interest in changing my iPhone simply for more screen real estate. My thumb navigation is quite comfortable, and the device fits my pockets comfortably. I don’t want to change my present iPhone experience.
I am, however, looking forward to see the adaptive design techniques that will likely be implemented in apps for new/varied screens. Because of multiple form factors, Apple is encouraging app developers to move away from fixed position design layouts. ∞