A while ago, while researching into editor frameworks, I asked a question on the ProseMirror discussion app about who is using ProseMirror.
https://discuss.prosemirror.net/t/who-is-using-prosemirror/1230/
As it happens, it looks like the NYTimes is also using PM, and they just posted this interesting article about what they have done:
https://open.nytimes.com/building-a-text-editor-for-a-digital-first-newsroom-f1cb8367fc21
The work looks great, unfortunately, however, I think the plugins they are discussing are closed source… I’m going to see if I can reach out to them and ask about it.