With Dragonflight focusing on both Wrathion and Khadgar, I would be really interested in having the legendary questlines back in the game.
Wrathion is the kind of character that you don't cross path with that often. We got to know him a bit more during BfA but I feel like a lot of people missed out on this narrative with Anduin and the MoP Alliance-Horde war.
The quest is mostly farming materials in this and that raid, but the little interactions that you get as a reward were pretty interesting. And same can be said about Khadgar legendary ring quests.
If it happens to just be a switch to trigger then Blizzard should definitely bring them back.