I'd actually like this. Different instances, not the same old boring cave, with different types of mobs even to be advantageous for different classes.
It could even be for exp as well so it'd be an alternative to PV. Though it depends on how much work and how easy it is to adjust the mobs' exp and loot in a specific instance.
Though one thing's for sure; the bosses themselves can't stay holding all/most of the ec, otherwise sins and ea's will just farm the sht out of it safely.
