In MoP I was able to use a druid heal for PvP with great effect, you could spam for several minutes before going out of out of mana.
For PvE I was able to use Resto Shaman, Earthshield on the tank, and chain heal for the rest to make it easy. The problem after watching some of those videos is for a fight you may need to be moving 50+% of the time. That really hinders the ability to dps or to effectively heal while standing in something bad.

Which is why I would really enjoy the Enhancement shaman to be effective enough to heal with the healing rains, and do the instant healing surges as top offs.
If average character HP is 2 mil, and 4x healing rain is 100k per second total. That's about a 5% hp heal per second. I don't know if that is sufficient. They should only be taking AoE damage, but no idea if that's enough to overcome some encounters.