And they likely will lose some customers as well by going to significantly larger screen, too.There have been more than a few polls in this forum with the majority wanting a larger screen. I would not mind them maximizing the real estate on the current iPhone as they could amd the screen bigger. Apple WILL loose some customers if they do not.
Can't have it both ways.
Unless perhaps they go for something like 3.75". It could be done without making the phone any bigger (or perhaps only a mm or two) but without being too overly large for a single average sized hand to reach all 4 corners of the screen.
Personally, I'd prefer >3.5" but <4".