I think a happy medium would be if you could export snippets of latex from a larger texmacs doc but I haven't actually tried it.
More in detail, all these papers are been written completely in TeXmacs and then converted to LaTeX to be put in arXiv: https://arxiv.org/abs/2004.09637 https://arxiv.org/abs/2004.01513 https://arxiv.org/abs/2004.00872 https://arxiv.org/abs/2003.14264 https://arxiv.org/abs/1912.06881 https://arxiv.org/abs/1912.04830 https://arxiv.org/abs/1906.11187 https://arxiv.org/abs/1812.04422 https://arxiv.org/abs/1810.12014 https://arxiv.org/abs/1805.10814 https://arxiv.org/abs/1708.03118 https://arxiv.org/abs/1702.03195 https://arxiv.org/abs/1701.07373 https://arxiv.org/abs/1610.07886 https://arxiv.org/abs/1508.03877 https://arxiv.org/abs/1502.00157
Similarly all the lecture notes in this page: https://www.iam.uni-bonn.de/abteilung-gubinelli/teaching
I think most of the discussion in this thread does not report any real current experience using it.
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.
In the TeXmacs editor Edit->Copy to->LaTeX (one might have to add some macro definitions in the preamble of the LaTeX document)