This editor looks really fantastic and could be a step forward to gain more fun with joomla.
I think the concept of editing code lacks by some long term development issues maybe bigger websites. It's the same problem which has other editors too.
Often in content management we need to replace old code with new one or need to repeat items with layout. So we need a solution, which can write template override layouts and fill in custom content or custom fields.
I would like to see my layout code separeted from the content. Twig is good for interpreted content and maybe we can connect reusable parts of twig-html with a json layout and configuration settings in the json.