If I listed everything it'd sound like I'm not happy with my X which I am, but nothing's perfect. I would be interested to see how much wider the phone would be if Apple stuck to a 16:9 display.
If you made the X (with the current screen height) but kept the screen 16:9, obviously the phone would be even wider than the 8 Plus. I'm not wanting to do measuring at the moment, but I'm thinking it may add as much as a half inch in width.
Personally, I'm one of those that is happy to have a similar sized screen to the 8 Plus (just difference aspect ratio) in a phone roughly the width of the iPhone 8. If Apple does make an "X Plus," I don't see myself ever buying it. Like mem0511, I tried an iPhone 7 and ended up returning it, I couldn't deal with the smaller text. The X seems close to perfect, for me, that way.
What I'd change is, first, I'd like to see the top bar (where the battery icon, signal strength, and clock are) to be blacked out pretty much all the time, to "hide" the notch. I don't need that bar to match the color of the app, unless the app is actually going to use that space for something useful; I'd just as soon keep a black bar at the top.
I'd also like to see an option to swap out the battery icon for a percentage, since you don't have room for both as on previous iPhones.