Bornakk revealed on the forums that gear will start having incentives to make you wear the appropriate type of armor. This means that holy paladins who are currently rolling on cloth and mail items will have incentives to stick to plate. What are these incentives? We don't know. It could be as simple as something like the current gem socket bonus system or a little more complex like a percentage increase in a particular stat. This could even be a generic spec based set bonus that gave you something if completely geared in class appropriate armor. We won't really know until more details are released.