I personally love all the pre-Lich King stuff. From Arthas finding Frostmourne and marching on Silvermoon City. Sylvanas’ story of how she was murdered and raised into the Lich King’s service, then eventually breaking free of him and possessing her old corpse. Perhaps with Blizzard’s new found love of “alternate” dimensions (it’s not time travel! /sarcasm) we could go back and revisit that. If not, maybe another CoT dungeon. Those are my favorite. Especially Old Hillsbrad and the Culling of Stratholme.
I think I would also like to go back and see how the high elves were, before they split off and half of them became addicted to fel energy. What story would you like to play through? Something from early Warcraft perhaps? Feel free to let me know in the comments down under!