Former AnandTech smartphone editor Brandon Chester says Apple had originally planned to use a type of organic light emitting diode, or OLED, display with a so-called S-Stripe sub-pixel layout, rather than the diamond sub-pixel layout that sacrifices the sharpness of the red and blue sub-pixels on the device.
In addition, Bloomberg's Mark Gurman says Apple had originally tested prototype versions of the iPhone X with high-refresh rate displays that would've made for a dramatically smoother user experience but cut that from the final product as well.
Today's iPhones have displays that update their contents at a rate of 60 times per second; one with a ProMotion display would update its contents at 120 times per second.
I believe that for the next iPhone, Apple will need to choose between implementing the S-Stripe sub-pixel layout it couldn't get working for the iPhone X, or it will implement the high-refresh-rate display technology.
My guess is that going with either will lead to higher power consumption, so while the company may be able to engineer a next-generation display to compensate for the inherently more power-hungry nature of one feature or the other, it won't be able to get both working in an acceptable power envelope.
If I'm right that it'll come down between the two technologies, here's why Apple should go with the faster screens rather than the sharper ones.
User experience and marketing
The move to an S-Stripe or similar sub-pixel configuration would increase the effective sharpness of the screen. It might even lead to a subjectively better viewing experience for most people.
But here's the thing: While Apple could market this new sub-pixel structure as increasing the effective sharpness of the screen and potentially improving image quality in other ways, it's not something Apple can easily market to the average consumer. Such a new subpixel structure would still result in an iPhone with the same marketable pixel density.
On the other hand, a high-refresh-rate display is something that's not only easier to market, but it's also a feature that customers can play with in the store and instantly feel the benefits of. Indeed, customers can go to a local Apple store right now and try out one of the new iPad Pro tablets, which come with what Apple calls ProMotion display, and they'll be able to see the clear benefit of this technology.
It's surprising to me that Apple didn't try to move heaven and earth to get this technology onto the iPhone X, if not the entire 2017 iPhone lineup, given that the latest iPad Pros have it.
One more thing
It's worth noting that Apple is reportedly planning to introduce three new iPhones next year: one with a 6-inch liquid crystal display (LCD), one with a 5.85-inch OLED to succeed this year's iPhone X, and one with a 6.46-inch OLED to sit at the top of the product stack.
Since the iPhone X with a 6.46-inch display will have the benefit of a much larger battery than the one in the 5.85-inch iPhone X, Apple may be able to squeeze a display with an S-Stripe or similar sub-pixel layout as well as a ProMotion display in such an ultra-premium device. The 5.85-inch iPhone X introduced next year could retain the same diamond-pixels structure but implement ProMotion, and the 6-inch LCD model would have a standard 60 Hz display.
Not only would Apple be able to get around potential power consumption issues this way, but since a 6.46-inch iPhone X could be a relatively low-volume, high-priced device compared with this year's 5.85-inch iPhone X and likely next year's 5.85-inch iPhone X, the technology and economics could work out.