This is my first time hearing of the "WriterDeck" concept, so it's very possible that I am missing some context, but... While booting to text requires less work and less packages, it seems like it has a lot of caveats. Firstly, it will likely be unreadable on any laptop that has a high resolution screen, and frankly even some old cheap laptops have one at this point, at least 1.5x~ish-scale DPI. Secondly, obviously better typography can be done in a graphical user interface, which seems like something you'd want if you're going to be writing on something. Thirdly, while the utter lack of distractions is admirable, this will also lack even the most crucial features and information. For example, I don't think you will even realize if your battery is about to die, which seems like it is a good way to accidentally lose a bunch of work. Battery state is probably the only thing that I really think it must show you.
It would definitely take a bit more work but a tiny dedicated graphical environment that functions as a basic text editor seems like it could go further. No particular need for Wayland or X11 here, either; you could get away with a simple Qt application directly on KMS/DRM.
Existing products include Freewrite and Pomera; there's also a pretty big nostalgia/retro space around the AlphaSmart, the eMate 300, and the Tandy 100. (As far as I know the pomera is the one that's linux underneath but completely hidden - it's particularly funny that it has wifi, but the only thing you can do with it is set the clock!)
It would definitely take a bit more work but a tiny dedicated graphical environment that functions as a basic text editor seems like it could go further. No particular need for Wayland or X11 here, either; you could get away with a simple Qt application directly on KMS/DRM.