I'd prefer to have them all from seperate new classes rather than the preexisting ones - I really don't like the idea of Gladiator having to choose between Dark Knight and Paladin. That kinda sucks...

If the Dark Knight were going to be introduced, then it would be better to have it as an evolution of something like an actual Knight class, with THM as the subjob.

If they were going to go with Thief, then they should have that as the basic class and have the Job be Ninja like it was in Final Fantasy I - the Thief could be a debuffer/DPS hybrid and the Ninja could be bulk DPS and stealth.

Musketeer really does sound very, very cool, though. For its Job it could have a Highwayman or a Gunner advancement - I'd imagine these as Debuffers which use their guns with specialised ammo to inflict Status Effects, like Guns did in Final Fantasy XII.

I don't know what to make of Arcanist, but I do like the idea of it as the pet class which would evolve into the Summoner Job. Ifrit and Garuda, and maybe even other FF Summons like Shiva and Bahamut on my side? Yes please!

The other classes I'd like to see would be Red Mage and Samurai. No idea what these guys would do, but I always liked their designs in the older FF games! Maybe if they introduce mounted combat there could be a dedicated mounted combat class, too - for lack of imagination, maybe a Chocobo Knight or something.