When creating a new structure, allow a new field type "link to web content".
When creating a new web content using this structure, this field would allow to search and select existing web content entries.
If the field is marked as repeatable, multiple entries could be selected.
In the database, such field values would be saved as article ids (plus group ids?). Templates could then decide how to display them - as direct links to content (get_article_content) or as links to predefined pages. Or maybe as links to page entered as a link-to-page field.
This would allow easy implementation of "links to related content" feature.