Earlier quoted context omitted.
Markdown is still just plain text without any "crazyness". Stuff like "## Header" isn't any more "crazy" than the ASCII art used in many Readme's of old and on top of that doesn't rely on specific monospace fonts or fixed width. And more advanced stuff like hyperlinks or tables are hard to do "right" in text anyway, since it's basically meta data without an objective "right" or "wrong" way of representing it. I also…
I have a 4k 43" monitor. Now I can easily see 8 separate chunks of code with my monitor split into 4 columns and 2 rows. Or I can see 2 columns and have the app on the left half of the screen with a debugger. I break the 80-char rule frequently, but having code be limited in width is still useful.
BTW I recently go a 24" screen (I was all about laptops, turns out I was torturing myself...) and I can easily fit 3 columns in Emacs, with a large-ish point size (238 chars across the monitor, DejaVu Sans Mono). If it's not a preference thing, and assuming (corrected-to-)fine eyesight, shouldn't 43" be capable of like 8x2 easily?