I think it would be neat if the next expansion took place in both the south seas and the emerald dream at the same time. They would be tied together by the main antagonist of the expansion: the old god N'zoth. N'zoth is both responsible for the emerald nightmare and likely to be imprisoned beneath the ocean.
N'zoth's prison would be beneath the well of eternity, which would actually be a titan device created in an attempt to keep N'zoth from ever breaking free. However, the sundering damaged that device by punching a hole through to the twisting nether in it, allowing N'zoth access to the emerald dream. Not only this, but the recent shattering would have damaged it even further.