I wouldn't object to a little better battery life which normally would mean a larger battery, but hoping the efficiency gains of a 7nm chip over the 845 at 10nm might provide enough.
Regarding camera, while I do continue to believe that Google could maintain class-leading photo performance with a single lens, I am hopeful that they add a 2nd lens to the rear to allow for wide angle shots or maybe integrate a 10x optical zoom (mechanics of which can all be done without increasing the camera bump - Oppo has already provided proof-of-concept). A 2nd lens also could enable untold wizardry via their AI/ML.
A bump in RAM is do, not so much because it is critically needed, but because it will provide a little more headroom for apps over the next few years, and the cost of same has come down a good bit now that higher RAM modules are more mainstream.
Other than that, I don't find that the Pixel 3 XL has any shortcomings that need to be addressed other than the obvious notch.
I do truly hope Google doesn't make a lemming move with an in-screen FPS, though. The rear FPS has been perfect in performance and in a location which is more functional ergonomically in nearly every instance (how often are you interacting with your phone on your desk without picking it up to do something other than check nature of notifications, which can be done without unlocking the phone?).