I recently discovered Tinker WriterDeck OS (https://tinker.sh/), which I’d been meaning to try, but this sounds like an even easier solution for repurposing old laptops and writing without distraction.
I'd put pdmenu on that with an automatic login. The user would jut have an editor, email assistant for mutt, net settings, lynx with gopher bookmars, mocp for music/podcasts, and maybe GPM for the mouse.