I am betting this year will be all about Internal and Spec upgrade. That is everything from CPU, GPU, NPU, Memory, NAND Speed, WiFI, Speaker, Antenna, Modem, Taptic Engine, Fast Charge Controller, Face ID 2.0, Camera, Display, and new iOS 13.
Basically apart from the looks and design, everything under the hood, including the materials used will be different in this year's iPhone.
While this is all just a guess, iPhone XS to iPhone 11 should be a better upgrade than iPhone X to iPhone XS.