hmm this is difficult but not impossible. What I imagine if this kind of system can be implemented is that classes can have multiple weapons w/c is similar to be open to lots of cross-class skills then after that jobs would have a specific kind of weapon. For example marauders would be able to wield axes and greatswords. Then when you get to choose a job u can either wield a axe and be a warrior or stick to the greatsword and be uhhm lets say berserker(though I think the job names would fit better if they swapped xD ).

As Im writing this I realized Arcanist has something like this with summoner and scholar. Yes both jobs still use books but they are job specific books. Just apply the same thing but with different kind of weapons which can apply different kind of play styles.