Well the iPhone X takes the current 4.7-inch iPhone's horizontal resolution, stretches it from 16:9 to 19.5:9, and decreases points per inch from 163 to 154 (same as the current 5.5-inch). If you apply the same logic to the current 4.0-inch and 5.5-inch models, you end up with a lineup of 5.0-inch, 5.8-inch, and 6.4-inch models. I think that will eventually be the lineup, but it will happen gradually rather than all at once.
I think their plan for next year will be to slide the 5.8-inch down in price and introduce the 6.4-inch model above it. How much they are able to lower the price will determine whether there are updates to the traditional LCD models or not. My guess would be that the 5.8-inch "iPhone 9" slides down to $849-899 and the 6.4-inch "iPhone 9 Plus" takes the $999 point (assuming the X is released at the heavily rumoured $999), and they will choose to price drop the 8 and 8 Plus rather than introduce four new models, going back to the usual two models per year (if the 5.8-inch somehow falls below $800 then this will DEFINITELY be the case).
I would guess that in 2019, the 5.0-inch comes along with last year's specs (like the SE did). That combined with the shuffling down the lineup of the OLED 9 and 9 Plus, and potentially another small drop to the flagship pricing with the "9s" and "9s Plus" (if they haven't yet gotten down to the 700s), eliminates the need for LCD models at the lower end of the lineup, and thus the lineup fully transitions to bezelless OLED displays.
I think the fact that the OLED model is being called iPhone X and not iPhone Pro suggests that Apple does not forsee a permanent place for a "premium iPhone", and this is merely a consequence of them being yet unable to deliver the phone they want to build at the current price points without taking a significant hit to their margin.