So part of the suggestion has been acomplished in the new patch:
- Players who have completed the appropriate quests related to looting the Head of Onyxia, Heart of Hakkar, or the quests involving killing Rend Blackhand will now be able to hand in a repeatable quest once a month to re-trigger these world buff effects. These new quests grant no rewards and confer no other benefits other than triggering the world buff event on your realm.
Source: Season of Discovery Phase 5 Patch Notes - Version 1.15.4