I've respecced my priests disc/holy a couple of days ago, and just wanted to share with you that this build is insanly effective.

pally is 38prot/23 ret and with sanctity aura, my priests are up to power infusion in disc and surge of light in holy.

I did a solo normal shattered halls run, and killed 18 elites in one pull, and everyone still survived :P

I was also able to do every boss in mechanar heroic exept the fireboss(didnt try it though) together with a friend (resto druid) with this build.

How it works:
macro trinket+PI+Inner Focus+Holy Nova

First pull a good number of mobs (10-15 normal elites if you have fairly good tanking gear) then get a bit agro with your pally, you dont need much since nova gives no agro.

Shadow word: deaht an elite, then nova to heal up+trigger your surge of light.

With this much mobs around, you are allmost certain to trigger surge of light on all of them, then instantsmite some mob. Holy nova again and repeat instant smite.

Sometimes its a good idea to renew the pally, but mostly holynova will keep him alive.

Your mana wont last as long as it would with 4 shadowpriests, but your aoedps+healing is amazing.