In a report from The Wall Street Journal (via AppleInsider), it seems that in 2018 Apple might not be going full OLED for their iPhones. Instead the report claims that Apple has “expressed interest” in buying Full Active LCD panels from Japan Display. The reason for this is that Full Active LCDs are said to be cheaper than OLEDs and are said to be able to match or even beat certain aspects of OLEDs.
It will also allow Apple to create devices with even thinner bezels as Full Active panels are flexible with bezels as thin as 0.5mm, half of that of OLED. As it stands the Xiaomi Mi Mix 2 uses a Full Active LCD, so it has made its debut in smartphones before. It is unclear if the use of Full Active LCDs means Apple will go back to using LCDs, or if Full Active LCDs are a temporary measure until they can secure enough OLED panels for use across their entire iPhone lineup.
It is also unclear if the successor to the iPhone X will continue using OLED, but either way take it with a grain of salt for now.