Unlike LyX, TeXmacs actually has WYSIWYG editing. LyX only provides a rough approximation of the output.
Moreover, the real-time typesetter in TeXmacs rivals the output of TeX/LaTeX. In some ways, it is better.
That said, I never use it for a document I'm going to send to collaborators unless they are really onboard with it first.
1. Emacs keybindings/window layout. If you aren't used to thinking in buffers and don't know which is the meta key, this can be very confusing.
2. TeXmacs uses TeX, not LaTeX, in the backend, though there are export/import commands. Makes it necessary to do some wrangling to get documents to match prescribed formats.
TeXmacs fails at usability right off the bat, even being unfamiliar to those used to Emacs keyboard chords (it's sort of implied in the name to be for that use-case), and I found it a little better after changing it to a CUA mode (I think it was called "GNOME Look and Feel"?). Finding crap in the toolbars and menu was obtuse, or even what all the keyboard shortcuts were. And then there was the fact that it was super-easy to crash and lose all your work in an instant. I found a particularly nasty case where just changing the type of header (chapter, sub-chapter, etc) crashed TeXmacs and caused all further attempts to open the file to crash the program immediately... grr
I would love if TeXmacs improves, or has improved, but I absolutely can't recommend it for serious work. Way too crash-happy, on both Debian and Windows systems. LyX is rock-solid stable, on the other hand (and has fewer "gotchas" due to its lack of WYSYWIG).
TeXmacs is also better for academia but most universities, conferences, and journals are behind the times... so graduate students and professors are still stuck with LaTeX.
if the above sentence is not followed by:
> "because [explain reason]"
my BS detector state is usually set to 'Red Alert'.
Moreover, the real-time typesetter in TeXmacs rivals the output quality of TeX/LaTeX. In some ways, it is better.
LyX does not intent to be a WYSIWYG editor. It is a WYSIWYM editor. It is the same as some people prefer Microsoft Word and others prefer Markdown.
It's confusing as hell, though.