I hate to be “that guy”, but the math for this just doesn’t seem to check out.
What resolution would those phones be? It couldn’t be 1920x1080 (“Full HD”), because at 4.7", the pixel density would be ~468PPI, and at 5.5", the pixel density would be ~400PPI.
So if both phones had a 441PPI display, they’d both need to have different resolutions, that are both kinda near Full HD, but not quite. And it means two new resolutions for developers to support, rather than just one.
This rumour just rings false to me.
Yeah, the PPIs are completely off. If the iPhone 6 maintains the current aspect ratio of the iPhone 5/5S (1.775), then a 5.5" diagonal iPhone would have to have ~474 PPI and a 4.7" diagonal iPhone would have to have ~555 PPI, assuming the # of pixels along the width and height of the phone were to double (from 1136h to 2272h and 640w to 1280w), as they did from iPhone 3GS -> iPhone 4, which is necessary to allow for a 1:1 pixel mapping for 3rd party apps (or, more specifically, a 1:4 pixel mapping), which would essentially require little to no additional work to make 5/5S apps work well on iPhone 6. If that ratio is disturbed, any UI, icons, and images used in 3rd party apps would have to re-mastered/re-created so that they wouldn't be blurry and ugly (e.g. graphics would bleed into unintended adjacent pixels, much like they do on unoptimized Android apps), and touch input could also be frustratingly inaccurate, since some apps depend on the specific 5/5S pixel coordinate system. The only other option would be to maintain the same total amount of pixels currently used on the iPhone 5/5S (727,040), which would subsequently require a lower-than-retina resolution for the larger screen size, which I don't think Apple would do.
So that means we need a 474 PPI resolution for the 5.5", and a 555 PPI resolution for the 4.7" in order to maintain the 1:4 pixel ratio.
According to Wikipedia, there currently exists only 1 commercial display that has a PPI at least as large as the minimum required for these screen sizes, which is the Vivo Xplay phone display that has a PPI of 538, which doesn't even seem to be used in any phone models currently, likely due to its high cost. There doesn't even exist a 555 or greater PPI display on the market that would be able to support the 4.7" display, which means the only option for that size would be to keep the same total number of pixels as the 5/5S, thereby lowering the PPI resolution to lower-than-retina, which, again, Apple would not do. Or, alternatively, Apple would have to invent a screen itself that has a 474 or 555 PPI resolution, which, firstly, they haven't historically made their own screens, and secondly, that would likely be incredibly expensive, and would almost definitely hike up the costs of the phone.
Therefore, this rumor seems to be totally false and mathematically impossible/improbable, and as much as I want a larger screen, I really doubt it will happen especially due to the fact that there are currently no displays on the market with a resolution at least as high as the minimum required resolution of 474 PPI, and if Apple would be the first one to implement such a high PPI screen, the costs for such a screen would likely be enormous.