Cool, but it's yet another case of re-engineering the same thing. (edit: its not entirely new). Splitting editors into an abstracted structure for finer control over data and presentation is something that's been done for a decade now in various text editors. Medium and Basecamp started similar projects and there's Mobiledoc which is trying to standardize the format. It'd be nice if all this effort focused on a singl…
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.