The change for priests is quite interesting, but the information is not enough to predict how this will affect the overall priest gameplay.
This is the idea that Blizzard have: " Discipline Priests are becoming more of an offensive healer. They will sustain healing through DPS, with another spin at the Atonement mechanic. Example: throw out single-target heals that place a buff on players, and the next time you Smite, they get healing. Players actively manage which buffs to refresh and make decisions as they go."
If this works as I think it would...Discip Priests will be the main choise for Arena healer in the new expansion. Trust me it's very hard to play against the now, so I can't even imagine how it would be if they become even more flexible in the next expansion.
In general very good change for the Priests and not very good for the players who will play against them.