What I think might be neat is a duty with gatherers/crafters AND the other disciples.

Example: Light party: 1 crafter OR gatherer, 1 healer, 1 DPS, 1 DPS OR TANK.
Duty: Escort crafter/gatherer to specified location and protect from oncoming mobs while the gatherer/crafter does its assigned task.

Monster difficulty adjusts based on whether the last spot is filled by either a DPS or tank (this is so queue times aren't terrible).