The yellow square marks the unused space. The magenta-colored line is drawn in the middle of the screen width.

Use entire screen width

Allow using the entire screen-width while writing articles.

On my 34" display with 3440x1440 screen resolution, HN doesn't even take half of the space.

I can imagine finding an option that sets the editor's and/or the content's width to 100%.

I don't know how you implemented the responsive design

..., for custom-domain blogs, and here on HN. So I could see some technical difficulties. I believe you solve them and reduce the need to scroll much when more than enough screen estate is available.