I used Emacs around 2010-2012 or so as a journalist, and I remember asking help on Stackoverflow regarding this exact same thing. I've lost my elisp multi-column-mode snippet; thanks for sharing yours. It was a really good way to edit a longer story; it's actually quite surprising that using something like this in a text editor is not that common. I later moved over to Plan9 Acme editor and IIRC implemented a similar solution there as well.

If you want to put the multi-column mode on massive steroids, check out an old Vim add-on called microViche for inspiration -- "text editing on an infinite pane": https://www.youtube.com/watch?v=9YNiPUTGO28 and https://www.youtube.com/watch?v=xkED6Mv_4bc

The addon itself, FWIW (no idea if it works on a current Vim): https://www.vim.org/scripts/script.php?script_id=4835

I remember trying to use this one as well, because the paradigm/concept is really cool and IMO unusual. I couldn't really get used to it, but it was a fun and inspirational way to make one's brain explode.