My guesses are:

-Summoner(might be connected to Guardian deities and the Primals(Still a Hunch))
-Musketeer(There's a Guild of it already in LL)
-Arcanist(There's a guild of it in LL too)
-Gunblade User(Garlean Empire uses it, also mentioned in some quests)

Samurai, or Ninja would be great too.