I wouldn't mind this happening actually. I think it would be frustrating at first but overall I it would make players better at their chosen job. I'm guilty of swapping classes like mad in and out of dungeons, so I'm not trying to be on a high-horse or anything.

The only problem I see with this is that the developers aren't so hot right now at balancing the melee-centric encounters with mage-centric encounters. (I'm not saying it is impossible to do runs w/ certain setups, but it is just much easier to bring all mages/ranged DDs.) What this translates as (unfortunately) is that people will end up excluded as melee are excluded altogether from dungeon runs and ppl will accept only mages and ranged DDs.

This idea is going to be destroyed by the community and you will be attacked personally before long. So steel yourself, my friend.