I am a reader, and there is nothing I love more than a well-written, intricate plot -- and nothing I hate more than reaching the end of the story, only to find some of those plot strings dangling unresolved, leaving me wondering exactly what happened. I run into the same problem with missing quests in WoW. There are a couple of quests that I desperately wish existed in the game for me to enjoy.
Where is Magatha? There needs to be a quest to find and bring back Magatha Grimtotem to justice, and it would be even better if you had the option of bringing her back dead or alive. My tauren would cut her down where she stood, while my blood elf would shrug and bring her back alive.
The Missing Eggs -- if you have read The Sundering, you know that Krasus rescued Blue Dragonflight eggs and set them outside of time to prevent them from being destroyed. I want to find them, to present them as the resurrection of the Blue Dragonflight and see it change the world.
With the Battlemaid visions of the past, I would love to be involved in things that occurred during the Shattering or the Sundering, to see what happened and be there (in spirit at least) for part of it.
What quests or storyline threads are dangling out there that you want to be involved in resolving? Do they take place in the past or the present? Who do you think escaped from their just desserts a little to easily?