As Kuo writes, Apple's been trying out a color electronic paper display (EPD) for the cover screen of foldable iPhones and also for future iPad tablets. That's no guarantee we'll actually get this on future folding Apple gear, nor is there any word on what Kuo's basing this assertion on, but using e-ink on a foldable is certainly an interesting idea.
Apple is testing E Ink's Electronic Paper Display (EPD) for future foldable device's cover screen & tablet-like applications. The color EPD has the potential to become a mainstream solution for foldable devices' must-have cover/second screen thanks to its excellent power-saving.May 17, 2022
An e-ink screen is quite different from the high refresh rate and high-resolution displays that current foldables use. The benefit would be far superior battery life. Just consider how long the best Kindles, which uses the same technology, can last on a single charge.
A regular e-ink display would be slow and unattractive to look at, even if it did use full color rather than just black and white. However, it could make sense if Apple intended to make the outer display a limited size panel like the Samsung Galaxy Z Flip 3. The e-ink screen could be used for notifications, static widgets and so on, leaving a regular foldable inner display as the main way to operate the phone.
Even though Apple has been quiet about any foldable projects, patents for its work have been found semi-regularly. The latest aside from the foldable iPhone are for a 20-inch foldable MacBook that utilizes an on-screen keyboard.
The first foldable iPhone is currently pegged for a reveal sometime between next year and 2025. If Apple's still experimenting with different display types for the foldable iPhone, then perhaps we should prepare to wait.