While it's still not clear whether Apple plans to release two new OLED iPhone models in 2018 or just a single one, a new report from Bloomberg suggests that Apple is working on a new design that will use a curved OLED display in its future phones.
According to the report, the display will "curve inward gradually from top to bottom" - so this design will be different then Samsung's popular edge-type phones, maybe something similar to LG's old Flex phones. Bloomberg also says that this technology is "2-3 years away" which is a bit surprising - by then Apple is expected to adopt foldable displays.
Bloomberg quotes "people familiar with the matter" saying that Apple does plan to expand the adoption of OLED displays in more devices - and will release an updated 5.8" OLED iPhone X mdel in addition to a larger 6.5-inch one. Bloomberg confirms that Apple aims to start use OLED displays made by LG Display in addition to the ones made by SDC.