Wonder how hard and how much people would like dual classes (and how hard it would be to code). Like making a barbarian/cleric or a mage/cleric. Something to think about.......
Make it twice as hard to level but imagine an avatar barbarian/cleric (sick).

If dual-classing were to become available on DL, not all benefits of each class should be available. In a sense, the avatar system we have now allows multiclassing but just in a logical progression and you can't choose what classes you multiclass into.

If you do barbarian/cleric, then berzerk, sanc and full heal should not be available. Also, the hit dice should be that of the cleric and not the barbarian. You would get the benefits of bash, push/pull, weapon proficiencies, healing, turn and detection spells. Would be very powerful, but not super powerful.