Apparently Blizzard either was or has been considering the Naga as an addition to the playable races, though their lack of legs is a big hurdle to overcome for things like armor design. In terms of future plot, the interview seems to imply that following Mists of Pandaria we will be headed back into mainland Azeroth, and that further story lines involving the trolls, the Burning Legion, and the Emerald Dream are slated to "gradually develop". Now, we know that an Emerald Dream expansion is something that many fans have been hankering after for a good long time, so this kind of news would be very much welcome to hear. Here I feel compelled to state that again, there is no official confirmation for any of this. However, there is one bit about the lore that I feel relatively confident is accurate, and that's Ghostcrawler's assertion that the relationship and conflict between the mogu, the Old Gods, and the Titans will be revealed in patch 5.4.
Happy speculations, everyone!
Update 10:42 p.m. EDT: 2P, the Chinese gaming site, has updated their English translation of the article noting that Naga will not be the next playable race. They also modified the way in which the next areas of WoW's content were talked about; however the three big areas (Trolls, Burning Legion, and Emerald Dream) are still areas in which Ghostcrawler noted content can expand into.