I'll quote my idea from another thread

How bout this..

lets say we are CON now...and when we equip blackmagecloth+wizardhat and equip Burn(or other R14 offensive spell) automaticaly new SP bar unlocked to class BLM. automatic trait that is [offensive spell+20%MagicPotency buff-10%Duration] while we on "BLM" title, the SP we get also goes to CON...so classing BLM also classing the base job CON

and lets say we are GLA...when we equip platearmor+heavyshield and we equip Cure we automatically titled as PLD..which it has automatic trait that is [Def+20% Healing Potent+10% Evade-10%]...classing PLD also ranking up the base job GLA...

just like that with bit tweaking...maybe we can add quest unlock or something...

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better idea: maybe trait that I mention can be used as "unlocker" opposed to equipping cure or spells, and to get it we must do certain quest.....
so basically you want to feel "Unique" by equipping gears that "themed" by that advance/specialization class... and to determines you can rank it, you must equip its trait(that we get from quest after fulfill certain Rank of job/jobs)