I suggested an idea to my son, who struggles greatly with the distraction machine. Even just having Microsoft Word open is bad enough because there are so many fonts, settings, the help system, and so forth. This, compounded by a bit of writers block, and probably the inherent boredom of the work.
I proposed to set up a Linux system with all apps disabled save for a plain text editor. I told him that it's not a punishment, but just a experiment in finding a practical solution to a problem that he acknowledges.
Your example of MS Word is interesting. Not only are these "playable" features distracting, they don't help with learning to write non-trivial texts either. I'd like to see them use a simple semantical text editor where they indicate the structure of the text, which then is automatically formatted. Formatting then is not a seemingly integral part of writing anymore, but a separate task.
More importantly, I think, is that a lot of educators and parents seem to value "having fun" as an important characteristic of education. I am doing research on innovative mathematics education in primary school, and, when asking teachers to evaluate the lessons or instructional materials, they always point out how much fun the children had (compared to the usual instruction). If I asked further and inquire about the actual learning of the students, most teachers aren't able to express anything beyond the superficial, either related to class management or to regurgitating parts of the curriculum.
The kids in my CS class use putty to access Ubuntu servers, then write up their coursework in markdown. The only way to view their formatted text is to look at the GitHub README.md files online.
As a result, there are very few distractions. They have putty and GitHub open on their screens, and nothing else.
FWIW, this is what a LaTeX editor might give you. You write paragraphs of text, with some tags to indicate the semantics of the text, and converting that into 'pretty' text on a page is (generally) a second step.
I was more thinking about something like LyX and hide the typesetting engine / markup language for a while. Although when children have experience with an editor like this, supporting them to learn something like HTML (of LaTeX) is probably a lot easier as they understand the concept of structural elements.
Depending on your son's age the Alpha Smart Neo (despite being discontinued) might make sense as an extremely bare bones word processor. I used an earlier model when I was in grade school and it was convenient for busting out first drafts and some light editing. The trick of the device, at least back then, was that it would present as a keyboard to transfer the text to a computer.
I proposed to set up a Linux system with all apps disabled save for a plain text editor. I told him that it's not a punishment, but just a experiment in finding a practical solution to a problem that he acknowledges.