it would be great to have an option to pop up the text editor of raw content element, something that looks like the Headline element Edit Text button:
But instead of a Rich Text tab, just the HTML, or even better, a CSS and a JS tab exclusive for the element, because usually I have to use a Div element as a container of raw content so I can add CSS to it (an then save the element later to use in other projects).
With something like this and the new components feature, this would be a powerful tool to create your custom elements.