We use CM at Overleaf[1], and it's been fantastic. To make it easier for non-LaTeX users to collaborate on LaTeX documents, we built our own rich text editor on top of it[2], which is still in beta. Still got a long way to go!
What was so cool recently was that a group of 7th/8th graders[1] used us to write their 300-page engineering notebook!! Just amazing :)
[1] https://www.overleaf.com/blog/289-the-nano-ninjas-building-r...
But, then again, shouldn't a single editor be able to handle those two usage-domains? (As this would mean the editor would be more powerful in terms of extensibility).
ProseMirror's model is structured. It's a nesting of elements strictly conforming to a configurable schema (by default close in spirit to Markdown - paragraphs/lists, emphasis, links, etc). Note that it's not "flat WYSIWYG" where each character/line has a style; a sub-list is actually inside the parent list, not just a bullet which happens to have higher indentation.
CodeMirror was started in early 2007. [1] ProseMirror is newer, announced July 7 2015 [2]. You've probably been using CodeMirror but didn't even realize it -- it's ubiquitous!
>CodeMirror is an open-source project shared under an MIT license. It is the editor used in the dev tools for both Firefox and Chrome, Light Table, Adobe Brackets, Bitbucket, and many other projects [3].
Check out the CodeMirror JavaScript, HTML and Markup code folding demo -- who could say no to that? [4]
[1] https://en.wikipedia.org/wiki/CodeMirror
[2] http://marijnhaverbeke.nl/blog/prosemirror.html