What about a synergist/saboteur? Might be cool to have a class that focuses on extremely powerful party buffs and enemy debuffs. Right now, these types of rolls are provided by others in the trinity, but the effects are relatively minor. 5%/10% debuffs and slight damage increases are common, but adding a non-healing support class might be kind of fun. I dunno, I feel like adding a new role would just break a lot of the game design (like 4 man dungeons and such), but it is interesting to think about nonetheless.