Blizzard wants the decision to use Divine Plea to be a tough one for Holy Paladins, not a no-brainer. Needless to say, Retribution Paladins and their 5k mana pool use it every time it's up. But when a Holy Paladin with 20k mana can recover 25% of their mana every minute, it's kind of an obscenity. So Blizzard is going to nerf Divine Plea by raising the healing penalty to 50%. Some people think this won't be enough to stop Holy Paladins from using the spell every time it's up, though. Rohan over at Blessing of Kings thinks the spell should not have a healing penalty but be canceled when the Paladin casts a healing spell.
It's an interesting idea, but it also doesn't make too much sense. He says that while 50% healing penalty isn't going to stop players from using the spell, he's afraid Blizzard might over-nerf the spell into uselessness. But if Holy Paladins can't heal through the duration of Divine Plea, that's kind of nerfing it to a 100% healing penalty, isn't it? You can remove the buff yourself, anyway, so that'd work like the cancelation he talks about. So how do you fix Divine Plea so that it becomes a strategic choice rather than be a natural part of a Holy Paladin's rotation?
The way I see it, Blizzard should stop looking at healing penalties and instead look at casting time. Prior to 3.0, a Holy Paladin's biggest weakness was that her bread-and-butter heals had a cast time. This punished healers during mobile fights, especially in PvP. When talents like Infusion of Light and Judgements of the Pure paved the way for crazy 18k heal bombs in less than 1.5 seconds, everything changed.
What if Divine Plea read "You gain 25% of your total mana over 15 sec, but the amount healed by your spells is reduced by 20% and casting time is increased by 100%"? A casting speed penalty might make the decision more critical in an environment where landing a heal on time is sometimes more important than landing a big heal. At any rate, we'll have to wait and see how Blizzard tunes this without nerfing the spell to uselessness.