I do like the concept of Disc in Cata: a true hybrid healer where your damage spells supply or augment your healing. However, if you enter a raid environment where maximum contribution is expected of every player, will there really be a role for a parttime healer?
If you take away the smite synergy in the tree, you basically have a far inferior holy priest with PW:B. Why would a raid want such a spec when it could bring a real DPS or a real healer?
I can envision encounters where raid damage comes in predicted bursts and Disc could help buffer in those intervals. Disc seems also set up to be a tank healer with shorter WS, Penance CD reduction, and Archangel. But every other healing spec is set up to be more versatile in Cata, able to fill every role. Is Disc going the other way?
I am definitely going to enjoy Disc in 5mans. I'm just not convinced it is raid viable.