At some point we might implement a suppress at the topic level which means no reply to the topic will cause it to be bumped, ever. This is called Sinking in Vanilla:
Sinking a discusion
By default, discussions are ordered by date of last comment. Sometimes moderators want to make a discussion ‘go away’ but don’t want to offend by deleting it or closing it to more comments. Sinking the discussion will make it sink down the page as others discussions are updated and created, even if that discussion thread gets new comments.
But I can’t see what you are describing implemented.