Being how Ninja is the next job @ 2.4 AND they've stated 3.0 will have a new healer and tank....
I'm thinking the gun Job will be one of these, perhaps utilizing gunblade as a tank (but that doesn't fully fit with the dual gun depiction they've consistently given us)
Not really sure which iconic Healer class/job they're going to go towards, but I'm looking forward to trying it out!
I want a blue mage type job, would even think it could be a tank depending on how they managed it. Gun Mage, however, could fit into the dual gun depiction nicely and I would be happy with that too!