In his overview of the October 22 Apple event’s new products, John Gruber relates the iPad sizes to the MacBook line, and adds this:
This, in turn, gives me hope regarding any potential move Apple might make next year with regard to a larger-display iPhone. What I don’t want to see is a single iPhone 6 with a larger display (and correspondingly larger physical size). What I’m hoping for is that, if Apple produces a larger iPhone, that it debuts alongside a 4-inch display iPhone with the exact same specs — same A8 processor, same better-than-the-5S camera, same storage capacities. Same everything, except for the size of the display.
If Apple can do this with the iPad, why not the iPhone too? The only complication I can think of is that with the iPad Air and Mini, both sport the same pixel count, 2048 × 1536. I’m not sure that an 1136 × 640 display at a bigger display size will satisfy those who desire a physically larger iPhone.
If a larger iPhone is, indeed, in store, I hope for a choice of sizes. But, once again, I don’t see the point of a larger-sized iPhone which can’t display any additional content on account of being equipped with a same-resolution display. While the proportional difference between a 4- and a hypothetical 5-inch iPhone is 20% — the same as the difference between the 8-ish-inch iPad Mini and 10-ish-inch iPad Air — the differences in what can be done in that space is not scalable in the same way. That is, while an iPad app can work on both display sizes with an identical interface, an iPhone app at five inches simply looks like a jumbo-sized version of the same app.
Perhaps I simply don’t get the appeal of a bigger iPhone, but I would think that its existence would be justified by more than an additional inch of physical area.