Well, I'm a fan of the 5 shadow priest idea too and would like to see how Morg does with it, but honestly the healing priests is intriguing too. Best way to tell how it would go is to try it. It's a a big investment to get 5 guys up but then again, that's what I call "playing the game". If you get it going, keep us informed as to the pros/cons.

On a related note, a bunch of us were playing priests and were taking the "long walk" to Badlands which for Horde involves crossing several ally zones. We had a comical pvp fight with 3 lvl 22-25 priests against one lvl 30 warrior. No matter who he attacked, they would turn "run away-kite-tank" and the others would stop and heal and dps. He'd stop, turn on the healer and we'd all switch roles. It took like 5 full mins to kill him but it was SO funny to watch. It was like watching a bear trying to fend off bees running around in all directions. Different, I know, from a single player but it still brings up an interesting question of whether it's a viable group build. Personally, I think it would be fun to try.