I have switched to a pure mastery gear build. For tank healing, our mastery is simply too OP now that it stacks. This style of healing is proving a bit odd to adapt to. I still find myself wanting to bomb raid members with direct heals while letting BoL aid with tank healing (as we did with our spirit/haste build in T11), but this is not very efficient with a mastery set.
With current levels of mastery (32% converting to a shield), my shields stack very quickly, and will nearly top out during short avoidance streaks from the tank. Utilizing the WoG>HS>HL priority (with DL being substituted for HL for heavier damage) on my BoL target, the tank healing has proven to be very stable. My raid healing contributions are almost exclusively from Holy Radiance, and for soft-enrage style constant AoE damage I will use LoD to assist further (DL directly on beacon to proc Tower of Radiance as well).
I find myself missing the haste as my casts are noticeably slower, but the results I have seen so far seem to legitimize a mastery/spirit suit with a ToR spec to support a tank healing role. It's early in the tier though, so we'll see how well this holds up in heroic FL encounters. I wont hesitate to go back to the spirit/haste build and INT gemming if it feels more appropriate for progression on a certain heroic fight.
"Faith is the assured expectation of things hoped for, the evident demonstration of realities though not beheld."