It looks like in 4.1, tranquility will be on a three-minute cooldown for restoration druids. Compared to the current eight-minute cooldown, this means it can be cast twice in a typical boss fight instead of once.
This strikes me as a gigantic buff for restoration druids. Now that tranquillity works raid-wide in Cataclysm, it's an emergency heal that can stabilise an entire raid. Ponder that a moment: a single healer, casting a single spell, can restore an achy almost-dead raid to being highly viable. As a bonus, the healing is a hot, so once your cast falls off you have several seconds to get regular hots up before the tranquillity hots fall off.
It's an amazing spell. Some effects can be trivialised if you have a druid available to cast tranquillity during it. If the effect happens twice, and you have two druids, then your raid doesn't have to be that smart to handle it. More frequently right now, tranquillity is an oh-dear button, if some players get out of range, or a healer gets silenced in some way, you can use tranquillity to get the raid over the hump.
Now that it will be on a three-minute cooldown, we can more frequently make plans to use it instead of saving it for emergencies. We can, for example, alternate shifting to tree form and casting tranquillity to have a big cooldown every minute and a half.
It sounds like we have another large buff, coming, too. I missed it earlier, but apparently the Blizzard designers want all healers to have a damage-reduction cooldown available.
Personally, I hope they don't make it a separate spell. I feel pretty good about how restoration druids work in Cataclysm, and I don't get excited at all by the idea of homogenizing the healing classes. To the extent Blizzard wants to work on druids' abilities to protect against incoming damage, I'd rather they focussed on our HOTs than on adding yet another ability on a cooldown.
A simple approach they could use is to let us cast barkskin on other players. Barkskin isn't as huge of a damage reduction as other healers get, but it's not shabby. Perhaps ours could have a shorter cooldown to compensate.
Another simple approach would be to increase the HOT portion of regrowth and increase the mana cost proportionally. Before a damage spike, we could add regrowth to the stack of pre-HOTs on the player.
A more fun approach would be to redesign living seed as our damage reduction. Right now, it's not something players consciously worry about, and its behavior is much like having an increased crit effect on our heals. One way they could make it work for damage reduction is to have the living seed grow first on the casting druid. Then, only when we cast regrowth on someone, does the living seed transfer to them and activate. Between damage spikes, the seed would grow and grow. When the spike finally comes, we'd toss on regrowth plus a sizeable living seed.
We'll see. I wouldn't be surprised if they simply add yet another spell to the mix, though I hope they can come up with something that keeps our spell count down.