Nature’s Bounty no longer affects Swiftmend, but now has a new effect. When the druid has Rejuvenation on 3 or more targets, the cast time of Nourish is reduced by 10/20/30%.
This is a great mechanic. When there's raid-wide damage to heal up, and we have to do it in a hurry, what we will do now is cast a few rejuvenates and then a lot of nourishes. As our mana gets more plentiful, we'll cast fewer nourishes and more rejuvenates, except for situations where rejuvenate is too slow. I'm not clear how often rejuvenate will be too slow, however. In Wrath, rejuvenate was plenty fast for just about everything except Infest.
Note that this doesn't entirely answer the challenge Xaar raised, tohugh, which is a little disappointing. Xaar claims that our heal-per-cast-time of rejuvenate is significantly less than that of the similar fast-raid-spam spells that other healers cast. His combat logs show him getting about 17k whereas other healers get well above 20k per cast.
Xaar's objection doesn't matter much for T11 content, because we will run out of mana anyway if we chain cast rejuvenate. It suggests, however, that we might come off as feeble in later content when mana is more plentiful.