I request adding a new MediaWiki system message that would appear inside the #bodyContent element, between #mw-content-text and .printfooter (if it exists) or #catlinks (if .printfooter is not displayed) tags, as seen in the image.
We expect to use it on Spanish Wikipedia to automatically show content from Wikidata (e.g. the table for authority control), but I think this is a useful feature that should be available on all MediaWiki installations.
This "message" would be empty by default and, as usual, its content would be determined by a certain page in the MediaWiki namespace.
For the equivalent header in #mw-content-text, see T151682.