I find it amusing that people don't see the 8/Plus as a significant upgrade to the 7/Plus
It is, in the same magnitude the 6s/Plus was to the 6/Plus, and the 7/Plus, was to the 6s/Plus.
It has all but the screen and form-factor of the X (if considering the Plus)
I think a lot of plus users are going to find the iPhone X smaller than they would like in screen real estate terms.
The X is only bigger than the plus in vertical real estate and even then its only marginal when you take into account the "ears"/status bar and the drag handle/UI button for home at the bottom of the screen. The width of the X display is exactly the same as the current 4.7 inch 6/6s/7 and considerably narrower than the 6/6s/7 Plus.