So, after reviewing screen size comparisons, here's what's coming next year

[sniffies]

After reading multiple threads about iPhone X and 8 Plus screen size comparisons, it's clear that iPhone X belongs to the standard family, not the Plus family (even though its display is 5.8 inches). Having been misled initially by the whole notion of "5.8-inch display is larger than 5.5-inch display", I therefore thought that iPhone X belonged to the Plus family. Not so. If you remove 8 and 8 Plus from the picture, iPhone X is replacing iPhone 7, not 7 Plus.

In 2018:

8 and 8 Plus are going away
Apple will introduce iPhone X Plus (or called 11 Plus) alongside X (or called 11) with various spec bumps + Touch ID and Face ID on both

In 2019:

This could be the year when Apple drops the numerical nomenclature for iPhones and just use Pro and non-Pro naming scheme, where iPhone has a 5.8-inch display (former iPhone X), and iPhone Pro has a 6.3-inch display (former iPhone X Plus from 2018)

P.S. There will be no 9

 

[hamiltonDSi]

That X Plus might be the 6" rumored OLED iPhone for 2019 that came up some months ago.
https://9to5mac.com/2017/05/23/iphone-9-oled-two-sizes/

So iPhone X (5.3") and iPhone X Plus (6.4").
Yeah that could work.