The second part of the interview is more general -- he talks a little bit about the next expansion (with the same speculation we've already heard: Gilneas, the Maelstrom, the Emerald Dream), and says that designing a race is tougher on artists, but designing a class is tougher on designers. He admits that because we had a new class in Wrath, it's unlikely we'll see another class so soon in the next expansion, but "not impossible" of course. And he does note that Blizzard tries to "pre-seed" the races before they use them as playable races, so if they are adding in races, chances are we've already seen them (which, you may note, wasn't strictly true with the Draenei in BC). Finally, he talks about the future of Blizzard's MMO in general, and says it's still wide open to them: they plan for the game to last for years, and what they do between now and then, whether that be more expansions, microtransactions, or even a free-to-play model, will have to depend on what they want to do at the time.
Very interesting interview. Chilton doesn't really reveal anything, but you do get the sense that save for a very skeleton plan of one or two years in the future, Blizzard is really playing it fast and loose with World of Warcraft. Even he admits that the game may look very different, depending on how things go, in another four years from now.