This was mostly wrapped up in the novel Stormrage. Malfurian destroyed the cause of the nightmare. This is why we see Malfurian and Ysera at Mt. Hyjal today. I could see a cool Cavern's of Time raid that goes back and allows you to participate.
More or less. The old god is still there, but he's "contained," not really dealt with. I could see them putting in the emerald dream in a major patch or an expansion. The zone is already in the game code (has been since vanilla), and you can see it on youtube vids, so I could see them doing something with it.
The area of Zul Gurub is empty, but I'm guessing/hoping that this (along with Kul'Tiras) will be dealt with by the end of the expansion.
However, is Zandalar and that piece of land north of Western plaguelands going to be touched on this expansion? And what is that plot of land north of WP?