I think WHM is going in a good direction with some of its design (not quite there yet but the idea is there)
- Have healing skills that stack to build a powerful DPS skill
- Have dps skills that can also build up to a powerful healing skill

Instead of the WHM healing bar filling by itself overtime, why not associating it to a dot where each tick is filling the bar to encourage healers to keep there dps dots on?
More skills should be like assize and have a dps and healing element to them.