Apple's successors to the iPhone 8 could have a similar bezel-less design as the iPhone X
Specifically, Apple is supposedly looking into a special type of LCD display made by Japanese company Japan Display called "Full Active" LCDs.
This type of LCD display would be less expensive and would run into fewer supply issues than the OLED display used in the iPhone X, two factors that surely contribute to the iPhone X's higher price tag compared to the iPhone 8 and iPhone 8 Plus. The iPhone 8 starts at $699, the iPhone 8 Plus starts at $799, and the iPhone X starts at $999.
Full Active LCD displays would allow for bezels around the display to be narrowed down to as much as 0.5mm. The LCD technology currently used in the iPhone 8, iPhone 8 Plus, and every iPhone before it requires "several millimeters" of space around the display, the WSJ reports. It could even allow for thinner bezels than the iPhone X and its OLED display, which need one millimeter.
You can see what Full Active LCD displays look like in some recently released smartphones, like the Essential Phone and the Xiaomi Mi Mix 2.
One thing to note about phones that use Full Active LCDs is that they still have a larger bezel that's usually found at the bottom. Judging by the design of these Full Active LCD smartphones, it's likely that an iPhone with Full Active LCDs could also come with a single larger bezel, too.
With all this said, nothing is set in stone regarding Apple's use of Full Active LCD display in its upcoming smartphones. This is also not a confirmation that Apple will introduce iPhones with this screen technology in 2018; nothing is official until Apple makes an announcement.