Holy Prism

Just to make the math easy, I'm going to say that the spell power is 20,000. Including tooltip, as abilities change. You can reference tooltip to compare with the ability above.

Holy Prism
40 yd range
Instant 20 sec cooldown

If an enemy is the prism, they take 14523 to 17750 (+ 142.8% of SpellPower) Holy damage and radiate 9794 to 11969 (+ 96.2% of SpellPower) healing to 5 nearby allies within 15 yards.

If an ally is the prism, they are healed for 14523 to 17750 (+ 142.8% of SpellPower) and radiate 9794 to 11969 (+ 96.2% of SpellPower) Holy damage to 5 nearby enemies within 15 yards.

Mathed:
If an enemy is the prism, they take 43083 to 46310 Holy damage and radiate 29034 to 31209
healing to 5 nearby allies within 15 yards.

Take that, reverse it for AoE damage.

@ 40 second mark the opportunity single target damage done is 129249 to 138930
@ 40 second mark the per target aoe damage done is 87102 to 93627
@ 40 second mark the 5 target (max) aoe damage is 435510 to 468135
4.5 second possible total GCD over the course of 40 seconds.

Upside: Best of both worlds (Able to be single target, or an AoE ability). Damage is immediate. Healing is part of the offense. Only level 90 talent that does AoE and generates threat. Ties with Light's Hammer in AoE damage at 5 targets or less.
Downside: 2 extra GCD's to manage in prioritization.

Noone seemed to mentioned it, but it should be noted, that Holy Prism does proc [spell=76669]!