Abolishing the class system is one of the worst suggestions one can come up with. Right now the armory system is what keeps this game very unique. The job system they are currently implementing is only the beginning of what could potentially be a dynamic job/class system.
One class isn't going to be one job forever. When the system grows we may see one class specializing into 2 or more jobs. We will also begin to see mix and match (2 class > x rank = some other job). Dropping the class system will only make this kind of specialization not possible.
A more practical scenario of why this specialization system could be nice. Let's say I'm an ARC fighting the Deepvoid Ogre in the current r45 dungeon. If I specialize to RNG I do more damage.. GREAT. But in the process of doing so I may lose the ability to use skills from LNC/CON/THM. In a fight like that, sometimes the situation calls for even DD to help heal and a ARC using LNC ws to reduce tp generation/stun makes the fight go much much smoother. But in the same dungeon, say a fight against the last boss Batraal, LNC ws become essentially pointless for ARC and dps becomes much more important. Then I can swap over as RNG to finish the fight. So yes, I believe that we SHOULD NOT abolish the class system.
And to those that argue why PUGs don't need mp, etc... right now this game is built to seriously reward those that rank multiple jobs. A PUG with stygian spikes/siphon MP from THM and Sacrifice/Cure would perform much better at soloing anything. Are you seriously going to wait for HP to regen or that long cooldown on second wind? If a party member dies and the mages are preoccupied keeping the tank up, any other DoW DD could essentially step in to toss a few backup heals or raise the dead member. The ability to bring skills from one class to another is one of the best aspects of this game right now.