There's the Muskateer's Guild located in Limsa Lominsa which has existed since 1.0 and remains there in ARR. There are even NPCs located inside the guild and is adjacent to the Marauders guild. So far though they've been very hush-hush about it and deny any rumors of muskateer being an unannounced class.
Edit: I should also add that Yoshi-P stated he wanted to add more magic classes before adding more DDs. Whether or not Arcanist and the two jobs that accompany it are enough no one knows. My guess is we won't hear anything about it until one of the first major updates.