I think there’s potential for something else, like supporting a way to insert external images via a specific UI, as you mentioned. I know it’s a stretch, but I’ve seen elsewhere the emoji action with tabs to search for GIFs or input external media, we could do something to improve this – it’s just not clear yet what exactly.
However, we do support some special input rules that make typing in the new editor familiar for people used to Markdown, like # titles or **bold**, so I’ve also added it for a  format:
It’ll allow you to type , and have yourself an image node.