Yep this is nicely done! We also use a similar block (or widgets) approach for our editor, and it works really well for mixing all kinds of content in one edit

Yep this is nicely done! We also use a similar block (or widgets) approach for our editor, and it works really well for mixing all kinds of content in one editor. Storing them as JSON objects with client-side classes that know how to render them also makes it really easy to add or extend the widgets later on.