Heh, for that exact reason I'm using it with my screen dimmed as much as possible and even considered adding a night[*] (black to red) mode for OLED screens (I write at night, I'm a vampire).
One of the use-cases I found when I was researching Ensō: there was a blogger who'd split writing into two steps:
1. writing with their screen dimmed as much as possible
2. editing the next day
Also, perhaps a pure-black screen with a simple indicator of the number of characters/words written would work here? You'd still know that the editor is recording your changes. Seems like a nice idea for a little app/toy.
The hotkey to return to my window manager is pretty hard to hit by accident. As for the writing app, it's just a python script looping over lines read from stdin and writing them to disk. Not many opportunities to do anything else.