It would be nice to allow JavaScript add-ins to expand or collapse a paragraph (currently performed when the user double-clicks a paragraph handle). When collapsed, the paragraph hides all child paragraphs.

Ultimately I'd combine this feature with tag access in the JavaScript API (another feature request) to create an add-in where users could tag paragraphs and then expand/collapse all paragraphs with that tag at once. Useful for showing/hiding related data across the document.