Two long established predecessors to this: Sir Trevor JS[0] and Colonel Kurtz [1].
I've used Kurtz extensively and it's been brilliant. The only downside of all these block-based editors is that you can't easily create layouts where images float to the left or right of text. Well, you can create them but you don't get a WYSIWYG idea of what it looks like right in the editor. I can live with that!
I've explored all sorts of editors and Colonel Kurtz is the one that's worked best: Trix, Draft, TinyMCE, CKEditor, ContentEditable, ProseMirror - just off the top of my head.