This is discussing one that you already had on your list; ProseMirror. In fact, you've had it on the list since 2015: https://gist.github.com/manigandham/65543a0bc2bf7006a487/429...

This is talking about using ProseMirror to build some more features into their CMS, but it sounds like more of just a use of ProseMirror rather than a new editor entirely.