I personaly am for an unlock system myself too, advanced jobs unlocked by doing the current ones up to a certain level.
The problem with such a system comes down to how to treat the weapons for them though at this point, unless you create a whole new class of weapons specificaly for the new job(which isnt too hard to do really)

Certain jobs kind of use weapons already in use so it seperates things a bit further, though im sure making weapons specificaly for them too, even if they are the same types wouldnt be too hard to do.