With the coming dual spec - priests will be the dominating force in healing. WIth a switch of a button they go from a top single target healer to a top grouphealer. No switching gear - nothing. It has already been announched that a raid of healing priests only should be able to do the 25 man content. That is offical from GC. 7 healing priests could become the norm. 9 healing priests in each guild. Thats alot easier to manage than to have 3 druids (2 get spot) 3 shamans (2 get spot) and 2 Palas (1 get spot). 9 Priests can easily switch around (2 taking time out each night) and you will never have to bother aobut changing strategies cause you dont have the exact healing classes to manage.
Gratz Blizzard on great job making WOW about one healing class only !