spoilers*
corsair/gunner dps: theres already a plack for musketeer in the coral tower of limsa lominsa. downstairs, they train in guns. merlwyb uses dual pistols. for your FC crest, you can already choose the dual pistol icon.
chemist: makes sense for the gunner's 2nd path- healer. the brother in the thurmaturge questline heals you with strange abilities, before he gets possessed. he's a chemist as he has no aetheric potential. also in uldah, is the alchemist guild.
puppetmaster: uldah has alot of mammets/puppets. halitali in uldah territory has alot of mammets. the pugilist guild is in uldah.
ranger: gridania's troops are rangers and lancers. we are just given bard, instead. also, one of king mog's moogles is a ranger. i think the U tribe in forgotten springs are also rangers.
thf/ninja: obviously from main story, it's basically a confirmation that their guild will be in limsa lominsa in a shadow/secret guild. hopefully, a thf can steal genji equipment from gilgamesh in future.
samurai: like someone said, during the doma refugee story, someone tells you to pick up scales. this hints at samurai, but no word or showing of a great katana at all.
red mage: alot of mobs use enaero, enstone, enthunder, etc. the code for the abilities are ingame. they are classically rdm abilities from ffxi. but no word or showing for rapiers.
far-out speculation:
maybe the civilzations that have fallen all hint at other classes.
dark knight: amdapori in Amdapor Keep seemed to have opened the voidgate, which the lambs of dalamud continue to do. maybe they will be involved in unlocking dark knight. the demons in amdapor keep and haukke manor use scythes, which can possibly be used by dark knight and
necromancer: sil'dih, uldahs sister city, resorted to raising their dead soldiers to try and win a war, which became their undoing. necromancer was a class in the iOS game Final Fantasy Airborne Brigade
geomancer: amdapor city (not keep) was supposed to be full of white mages. but the city is like an ecosystem gone awry, while the central tower is full of voidgate monsters. also the thousand maws of totorak, which used to be a jail in south shroud, is filled with "eco-monsters".