When did they actually say acn and msk would be the first two out? ACN came out first because it won the poll of what most players wanted, and also because we needed another healer. I dont remember what came second but people have been asking for a dual wield thief/ninja for a long time and seems a lot more widespread than gunner. Although I would have liked to see gunner too, it MIGHT come out before the expansion but after rogue, they brought it up after all and said its 'not what we're expecting'. Otherwise most likely the expansion, along with the tank and healer classes they are talking about.

But then hey, they might be saving it to announce it later at E3/the next live letter in a few days.