Because NPC path-finding is a mostly server side operation (has to be or NPCs would use different paths on different clients), this turns out to not be significantly easier than adding full on collision.
The improvements we are currently working on are: 1) getting NPCs to prefer to spread themselves among available targets, rather than all clustering on a single target, and 2) getting NPC movement to look less spastic. Obviously we will continue to improve avatar combat as much as we can going forward, but these are going to be our first steps.