Over at Forestry.io we replaced our markdown editor with a Prosemirror implementation!
Forestry is a CMS for Jekyll & Hugo sites, so having a great text markdown editor is really important to us. We used to use medium-editor but it caused a ton of problems for our users.
We’ve been using it for a couple months now and things seem to be pretty stable. There are still a few issues that haven’t been dealt with, but they’re all relatively low priority for now. Overall, we’re all very happy with Prosemirror so far!