Symbiosis (Mastery) has been removed and replaced with Harmony. Harmony increases direct healing by an additional 10%, and casting direct healing spells grants an additional 10% bonus to periodic healing for 10 seconds. Each point of mastery increases each bonus by an additional 1.25%. Healing Touch, Nourish, Swiftmend, and the initial heal from Regrowth are considered direct healing spells for the purposes of this Mastery. All other healing from druid spells is considered periodic.
This is what Symbiosis currently looks like:
Symbiosis: Increases the potency of your healing spells by 11.6% on targets already affected by one of your heal over time spells. Each point of Mastery increases heal potency by an additional 1.45%.
So, this is just my interpretation, go to Elitist Jerks for solid math please. Instead of getting an 11.6% boost to healing spells on a target with a hot already on them we get a slightly less 10% boost for the direct healing spells regardless of target just for choosing the Resto tree and then 10% on our hots as long as we weave in direct healing spells every 10 seconds to keep 100% uptime on the buff. A bit of a limitation on mobility perhaps but if you use Swiftmend every other time since it's on a 15 sec CD you just need a direct spell every 20 seconds and that's not a problem.
That should mean a bit of a boost to Tranquility, no? You should always have used Wild Growth to get stronger ticks while channeling but now you're not dependent on having hots up on particular targets, I mean health pools change and people get out of range. You should use a direct heal within 2 seconds before starting to channel Tranquility though since it's 8 seconds long and you are guaranteed full mastery benefit on this one.
The mastery potency is nerfed from 1.45% to 1.25% but I guess it's still a buff since it will benefit more often than what it currently does since we do a fair bit of healing on targets with no hots anyway. I approve (I think). I'd rather weave in a direct healing spell now and then to keep a buff active than be limited to only benefit from healing those that I'm already healing.