The Wall Street Journal reports that Apple plans to finally drop LCD from its iPhones in 2020 - and to use OLEDs in all of the models.
WSJ also says that Apple plans to release an ambitious 2020 iPhone lineup with "a more flexible handset design". The 2019 lineup will be an "iterative change" from the current Apple lineup - and will still use an LCD in the lower-end model.
Apple's current 2018 OLED iPhones are the iPhone XS with its 5.8-inch 1125x2436 flexible notch-type AMOLED display (produced by Samsung Display), 4GB of RAM and 64/256/512 GB of storage. The XS Max has similar specifications - but with a larger 6.5" 1242x2688 AMOLED.
Display experts from DisplayMate rated the iPhone XS flexible AMOLED as the world's best mobile display, on par with the Galaxy S9 and Note 9 displays. Display Mate says that Apple's AMOLED display (made by Samsung display) has a close to text-book perfect calibration and performance.
The OLED on the iPhone XS uses an LTPS backplane. Interestingly for the 2018 Apple Watch Series 4, Apple adopted its own patented LTPO backplane technology for the AMOLED displays. Low-Temperature Polycrystalline Oxide (LTPO) combines both LTPS TFTs and Oxide TFTs (IGZO, Indium Gallium Zinc Oxide). LTPO can be around 5-15% more efficient compared to the currently-used LTPS backplanes, but is more complicated to produce and may have a lower pixel density. See here for more information on LTPO. It will be interesting to see whether Apple will adopt LTPO in future iPhones as well.
Apple is also looking into Micro-LED display technology, but it is likely that Micro-LEDs will be first adopted (like LTPO) in wearable displays and only later brought to the company's smartphone lineup.