What a very happy surprise!
I for one am very happy to see CodeMirror’s facet system come over — we were even trying out some very anemic ways of expressing dependencies on other plugins in ProseMirror, and yearning for that api.
The new change model sounds pretty interesting as well. We build a number of features on knowing what region of the document has changed for performance reasons. And I remain interested the idea of document projections, where schema composition will make a number of tricks possible.
What sort of feedback are you looking for at this point, if any?