With less than a week to go until Apple's (NASDAQ:AAPL) September 2015 keynote event, the rumor mill has reached a fever pitch. Speculators have called for Apple to unveil everything from an iPad Pro to a new version of Apple TV, iOS updates, and an updated iPhone line.

Whether any or all of these reports have merit remains to be seen. But there's one in particular I don't believe: namely, that Apple's newest iPhones will feature OLED displays.

Don't get me wrong: As a longtime shareholder of OLED specialist Universal Display Corporation (NASDAQ:OLED), I'd love nothing more than to see Apple shift away from the LCD displays its current iPhone models employ. Heck, a few days ago, I even singled out Universal Display as one of five top stocks to buy this month. But I didn't choose it because of an imminent expansion further into Apple's repertoire. 

I do believe Apple will eventually shift its products lines to OLED. Just not yet.

The rumor has merit
Driving the latest speculation was a purported leaked image of the new iPhone 6s Plus. Specifically, that box shows the phone with a picture of a koi fish on the screen, which led some industry watchers to suggest the iPhone 6s may feature motion wallpapers similar to those used in the Apple Watch. However, the additional graphics processing used for such motion wallpapers unavoidably drain the device's battery more quickly than static images -- something for which the Apple Watch's power-sipping OLED display may help compensate for.

Apple Watch Motion Wallpaper

A motion wallpaper on the Apple Watch. Credit: Apple.

That's not to say motion backgrounds for the iPhone would be a surprise. When The New Yorker published a profile of Apple Chief Design Officer Jony Ive this past February, Ive lamented that the iPhone 6's static wallpaper approach "feels very, very old" compared to its wrist-worn colleague.

The New Yorker wrote: "He went on to explain that an Apple Watch uses a new display technology whose blacks are blacker than those in an iPhone's L.E.D. Display. This makes it easier to mask the point where, beneath a glass surface, a display ends and its frame begins. An Apple Watch Jellyfish swims in deep space, and becomes, Ive said, as much an attribute of the watch as an image."

Ive's mention of the Apple Watch's deep blacks was an obvious reference to the fact that OLED materials emit their own light when excited by an electric current, so they don't require a backlight. This allows designers to individually turn off unused pixels in an OLED display, eliminating the slight haze emitted on black screens by competing backlit LCDs.

Wrong timing
On one hand, this seems to indicate that Apple has a desire to transition to OLED for its iPhone line. On the other hand, I'm not convinced the supply chain is ready for such a transition.

First, consider that, in January this year, Apple reportedly contracted longtime suppliers Foxconn and Innolux to build a $2.6 billion OLED display factory for both wearables and a roughly five-inch smartphone. But according to sources familiar with that situation, the target for mass production at the factory was either 2016 or 2017.

Lgdisplay Flexible Oled

One of LG Display's 5" flexible OLED screens. Credit: LG Display.

Meanwhile, in March 2015, Apple made a billion-dollar prepayment to help build and secure exclusive capacity from a new LCD factory run by Japan Display. This factory has a targeted opening of 2016, which prompted analysts at JPMorgan to speculate that Apple would almost certainly keep using LCDs for at least one more model iteration of iPhones.

Finally, in July, LG Display (NYSE:LPL) announced it would invest nearly $900 million in a new production line at its plant in Gumi, South Korea, for flexible OLED displays. LG Display is currently Apple's top supplier of similar flexible OLED displays for the Apple Watch, and consequently counts itself as Universal Display's second-largest customer behind Samsung. So its move to aggressively expand production serves as yet another indication of an impending shift by Apple for OLED to a larger product line.

But here again, LG Display's new production line isn't scheduled to start mass production until the first half of 2017. This means that the earliest Apple would be able to secure enough OLED display inventory to meet demand would be later that year.

While I still think Apple wants to reveal an OLED iPhone as soon as possible, I'd be absolutely shocked if it does so at next week's keynote.

Steve Symington owns shares of Apple and Universal Display. The Motley Fool owns and recommends Apple and Universal Display. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.