It looks like this:
https://i.imgur.com/6Zw2fyr_d.jpg?maxwidth=640&shape=thumb&f...
https://i.imgur.com/6Zw2fyr_d.jpg?maxwidth=640&shape=thumb&f...
At 25 character columns it will also look rather awful on desktop or widescreen monitors.
Borrowing from email etiquette I find using > arrows to be most indicative of quotes, although HN sometimes eats newlines for breakfast.
Same for too wide lines.
The ideal length of a line is somewhere between 50 and 70 characters.
Readable != Good Writing
This is not an issue if you don't use codeblocks, the browser is then free to reflow the text as necessary. If you use codeblocks the browser cannot reflow (by default) and you make the entire UX worse.
The HN format captures the most important parts of MD; italics, code and ALL CAPS.