So I think it's safe to say that the World Quest system is the best daily quest system ever implemented in WoW and both Blizz as well as players are for the most part satisfied with the way the system works.
I'd be extremely surprised if they ditch this in the following expansion. I think they will most likely expand on it instead.
With that said, how do you think they will evolve it in the following expansions?
I personally would like to see it work more closely to how it does in GW2. Where there are areas (phased and non phased) that get attacked or requires you to do something to complete the quest. In GW2, you don't actually need to manually join a group, everyone within that area contributes to the quest. You can choose to solo it or work with other people. It feels much more fluid than how they work in WoW now. The GW2 quests aren't perfect though, for starters if they are completed they will go away for EVERYONE. So it's like a phased event and once the problem is solved (invaders are killed, dragon is slain, nuts are picked up and squirrels are shoo'd) the quest goes away for everyone and you'll have to wait until the event triggers again. This makes the world more realistic, but it also means you can miss a quest so they'll have to do away with the current Emissary requirements if they go this route.
Overall, I still think it's a better system than the WoW WQ, and would be a natural evolution to WQs.