It'll be like Cata healing, if you had 2-3 times as much HP in Cata.
I think it's a great idea, I hate the way healing is binary - you're either full HP or about to die. Means things like hots, single target heals, Shaman mastery and triage healing become irrelevant and we're playing a degenerate gameplay where absorbs are kings of the meter simply because they apply first in the game logic (which incidentally means you overgear the content).
Instead in WoD, if someone's at low HP that doesn't mean they're going to die in a second. You don't have to keep everyone topped all the time, instead you choose how you want to heal and how much mana you want to spend doing it.