I'd love to see chemist as it fits the castle theme so well, but not as a gun wielding class, its a waste to use an iconic dps weapon on a healer, when weapons are only tied to one class.

There is no system that could viably work that doesn't make the gun do bugger all damage and just not get used, or do too much damage and make chemist unbalanced against the other healers.

I'd prefer it is Dark knight was a great sword DPS class, I just can't picture the hp sacrificing DRK that would bring in some interesting mechanics as a tank, doesn't fit the bill for me.

On the tank side though, a templar, mystic knight or Samurai would be cool. (I'm not suggesting the samurai would be set up in ishgard)