Would you even notice that many pixels during day-to-day use? It's unlikely that you would. Really, at a certain point, on screens designed to fit into your pocket, there's only so many pixels per inch you're going to be able to spot. With most high-end smartphones offering high-resolution screens, this seems like less of a selling point going forward. Size and brightness--and how those things affect battery life--seem like more pressing concerns.
If there's a phone doing something unique with its display, it's Amazon's Fire Phone (which is not exactly selling like hotcakes. The Fire Phone features a display with Dynamic Perspective, where the phone adjusts what's on the screen to reflect where you're looking. (Rotate your head in the Fire Phone's Maps app, for example, and you can get a close-up view of some 3D landmarks.)
What Apple might do: If Apple does wind up producing larger phones, it's also going to have to come up with enough power (most likely via a higher-capacity battery) to let that screen shine in all its Retina Display glory.
Phone makers are eyeing durability
What Apple did: Touting how its phones stand up to the rigors of daily use has never really been a part of Apple's sales pitch when it takes the wraps off new phones. (For that, you can do a web search to see people inflicting all sorts of damage on their iPhones in the name of science.) While Apple generally keeps a tight lid on who supplies the parts for its devices, it's widely assumed the company uses Gorilla Glass, the glass cover from Corning that helps resist scratches, as part of the iPhone's screen.
What's happened since: With smartphones becoming a more essential part of people's lives, phone makers have turned to durability as a possible selling point for their devices. That's certainly been the tack adopted by Sony with its Xperia line of smartphones: the latest version, the Xperia Z2 can be submerged in up to 5 feet of water for half-an-hour without suffering any damage.
What Apple might do: Apple's relationship with industrial sapphire maker GT Advanced Technology--the two companies have teamed up on a sapphire crystal plant in Mesa, Arizona--has led some (OK, me) to speculate that Apple's next smartphone will incorporate sapphire--the hardest natural substance after diamond--into its screen. If Apple does that (without driving up the cost of its phone), durability could become a larger part of the iPhone's story.
You can do more with your finger
What Apple did: Arguably the biggest addition to last year's iPhone 5s was its TouchID fingerprint sensor. The feature lets you unlock your phone with just a touch of a recognized fingerprint. It's not a bullet-proof security measure by any means, but it certainly makes it easier--and a little bit cooler--to unlock your phone.
Sign up for CIO Asia eNewsletters.