Disc priest healing is a beast now - its so damn good, that its borderlineing OP.
Spirit Shell is the revival of shield spam - its just applied way easier.
Coupled with atonementx5 stack and PI it reaches a burst healing potential, where the other healers can only glare - and thats with 0% overhealing.
Coupled with way better regen than ever, disc is in a really sweet spot.
I recon Spirit Shell will get relegated to a 2-3 min CD within.. well, short time..
Unless, the damage intake will go through the roof in MoP, where a 1min cd would make sence... though, all indicators are, that healers will have to fight(Snipe heal) for their healingmeter place there, as it has been the last 8 years.