Just as a note, I do use it today, just not to publish anything as I mostly have to adhere to journal article styles (can't just get by on preprints in my field) and I collaborate with others.
Most of my presentations are also written in TeXmacs and in these days I use it to teach via Zoom, or to discuss with colleagues/students, make computations, etc... Not really using paper anymore. If you need to do algebraic manipulations, then it is more convenient to copy/paste on the screen that to rewrite the same equation several times with small variations on the paper.
Using the submission requirements as an argument seems so wrong to me, it is like saying: since the final format is PDF we need to write our ideas directly in PDF... if one day editors will decide to use XML as submission format, then what? I do not want to think about mathematics with a screen divided in two parts, and the quality of the process is also very important to me. I spend maybe months to work on a paper in TeXmacs and at most only 1h in LaTeX when I really need to because editors are become used to require from the authors the work a professional typesetter would have done in the past.