Now, before I get down to this. Let me explain what the title means.
Attonement Priests are well known for DPS'ing and healing both at the same time, and I believe there is potential for Enhancement Shamans to do something very similar.
In my guild's current raid group, we sometimes have issues with getting enough healers for our raids, and we want to use a healer less for some fights so that we are able to bring more DPS'ers to our raid group.
I feel as if using an Enhancement Shaman to heal with the right Talent and Glyph choices could be viable, even more so when 5.3 is released. Look at it this way;
We gain Spell Power from Attack Power, meaning no gear has to change.
Our Maelstrom Weapon glyph allows us to gain increased healing.
Echo of the Elements allows us to gain duplicate heals for no additional cost.
Our current 2-set bonus allows us to gain the cast speed for these heals a lot more quickly
Ancestral Guidance scales with the Glyph of Flame Shock, Healing Rain and Chain Heal spam glyphs while we are still dealing consistent damage.
Mana would never be an issue
I feel it would be useful on a lot of fights where healing isn't a large issue when you're dropping a healer, but it's still of slight concern. And with 5.3, we gain an additional 10% Spell Power from Attack Power which would compliment our healing potential further.
I'm curious, I've managed to top healing meters in LFR before and I can see the potential for 25-man Enhancement Healing, but I think it could work but not as well within a 10-man environment also and I would love to see it happen.