Class =/= Job. Classes are more difficult to release because it requires the guild house to go with it. I'm sure musketeer will be along soon though because Merlwyb's character model is obviously a musketeer. Though I would not expect such a change until after 2.2 at least.

As far as new Jobs are concerned, they can easily be added because all it requires is an NPC and Job crystal. They can also be built on the classes that already exist. I personally believe a new STR based tank classes to be released for the LNC class. The guild quests for the Lancer's guild seem more tank related than DPS. As far as a new DEX based class, maybe a Sharpshooter job for archers?