@marijn great work with the node views! Seems you are on the right track with implementing custom elements. Something that I referred at Schema API design
So can we now use the node-views to define fully our own custom elements? maybe with special design-time/runtime rendering and custom inline inspectors.
I like your codemirror example - but maybe a more generic example will be to implement a simple photo gallery/slider as inline custom element. When being edited the gallery will present custom ui (in it simplest form just be able to drag new images. Something that is like for example https://github.com/orthes/medium-editor-insert-plugin for https://github.com/yabwe/medium-editor
So a gallery is a good example of self contained element. However there are some other elements that only need to be extended. For example if you are editing some Bootstrap framework elements - you only need to add custom classes to existing html elements.