I tried theorycrafting it out myself a while ago. The conclusion that I came to was that you'd need to use consecrate or you'll have too much downtime which half defeats the purpose of going holy for dps as you can just go ret if you're in melee range. The problem is it doesn't take long until all of your abilities are on cooldown and thus you have downtime. Another minor problem is itemization, considering that you gain nothing from haste since everything you use is instant and the GCD reduction isn't going to matter since it doesn't reduce your cooldowns. Should work really well for questing though.