As a resto druid, that sounds like a neat idea. I'm spending every GCD applying HoTs to people who need them.
But as a resto druid, I'm a little corn-fuzzled as to how Ulduar raid damage/tank damage is going to shape out to be.
With harder raid content comes higher burst and raid damage. In Sunwell, you couldn't afford to stop and think about if your mana pool will be able to take the hit, you heal or they die. (not to say that Ulduar will be as hard as Sunwell pre -or- post nerf, I think we all know that it wont.)
If they want us to consider how much mana we have, and how much we'll have after we cast our heals, then either:
1) They'll be nerfing mana regen across the board, while keeping raid damage at a moderately low level, in which case raid content won't be any more challenging without the use of cheap "Raid walks to point A at time X" gimmicks for every encounter.
2) They'll just expect healers to wait until someone is down to their last 20% before we heal them while upping burst and raid damage.
@ number 2, I've gotta say: "HELL NO!". New content on the same day as MP5 nerfs is A-ok with me. (to be honest, waiting 5 seconds to proc a free 1400 mp5 is ridiculous) But they can't just expect us to redesign our whole healing mentality as well, when people take damage, we heal them!