This should so be a druid spell. Common.
Healing Rain (level 83): An area-effect heal-over-time (HoT) spell that calls down rain in a selected area, healing all players within it. There is no limit to the number of players who can potentially be affected; however, there are diminishing returns when healing a large number of targets, much like the diminishing returns associated with AoE damage spells. This should give Restoration shaman another healing tool that improves their group-healing and heal-over-time capabilities. 2-second cast time. 30-yard range. 10-second duration. 10-second cooldown.
We better get something even more awesome.