Just a thought, but perhaps we can have our cake and eat it too...

I for one, am for class specialization. I would like to play a Conjour and based off of the specialize system, turn my Conjour into a white mage, or a black mage. I think that would be a lot of fun. But that's not to say we can't also have "unlock-able classes/job - Advance jobs/classes".

I think that if done right, both systems would work well together. Why can't we have class specialization into Jobs and then down the line, add in quest lines that unlock other classes, or better yet unlock other specializations for that class. For example:
The conjour would have two paths, black mage, white mage.
After completing a quest the conjour could then upgrade their white mage path to white wizard. (Much like from Final Fantasy I) - Just a thought. And the same would be for the black mage.
Or, based off of your levels on specialization you could open up new paths on other classes... (But this might be way to complicated)

Anyway, I would like to see some type of specialization system within the class system, and that people could search and see you by your specialization which would give parties the roles they need to play.

I also hope that the interface for specializing in different jobs is pretty slick, something as pretty as the character creation system.