To be honest I can see them moving away from the armoury system where class=weapon as we know it with jobs. I think it will be kind of like FFXI in that jobs can use different weapons and as you get skill ups with them you get better with that weapon.
The difference here is that weapons house more than just weapon skills they have abilities, skills and spells too. So in FFXIV it would make a bit of sense for the weapon to unlock the job but then not necessarily be tied to it as the job will already house the skills learnt from the weapon.
Maybe they will make Job/class like Job/sub Job so say you were PLD and picked a sword you would be PLD/GLA which would be a traditional PLD really with lots of defence and enmity abilities.
However say you had your job as PLD but equipped a LNC so then you would be PLD/LNC this would keep the core PLD skills but you would lose the skills that GLA brougt to the traditional PLD role. As a PLD/LNC you would gain skills from the LNC side and play the role of PLD differently.
Obviously some combos are going to be better than others but it would be nice to have the flexibility to try them out.