What if all browsers suported single page split view? So that the left side was your regular view, half width, and the right side was the continuation of the same page, where the left side ended.
+ 1.
Our two eyes are placed horizontally, giving us a landscape field of view. Yet, left-right eye movement/tracking is limited, so print or online reading material is mostly portrait. I guess we did not really evolve for reading! :-)
The book printing industry did not face this problem as they print on both sides of a page and then position these as the left and right pages of an open book! And sometimes also use of multi-columns formats when using wider papers (e.g., newspapers) or smaller fonts (e.g., journal papers).
Could someone not create a browser plugin that automatically lays out the content onto the left and right sides like a book? How would scrolling work is a question, as also asked by a comment here [1]. Do we really need scrolling? Aren't page flips just sufficient? :-)
I work on a 16:9 27" display where this is moot (still, I feel like I use the center 50% of the display 90% of the time) but I feel this pain in laptops.
At 16:9, for page-based content (all text editors and code tools, productivity tools, web browsers; terminals less so), you're forced to display two pages side by side. Still, they're shorter vertically than your eye can handle. Horizontally, your eye will either gravitate towards the center of the display, or have to switch between the two sides (ultimately rendering the extra area of the display temporarily useless)
At 4:3 in full screen (especially important for smaller displays) you can have a sidebar or ancillary tool occupying 1/3 or 1/4 of the screen, and the paged content occupying the rest.
I've made my peace with 16:10.