If we introduced it like the 2nd exampled it would be a DPS and Utility mastery. Mastery rating could increase the healing and the extra holy damage.
And yes I didn't mean +holy damage but an additional 1-2% of your attacks is added on holy damage like Necrosis and shadow damage for DKs. It would act much like the old version of flametongue weapon, granting the group a holy damage proc. You could even increase the numbers, but give it a 40% chance to proc each attack instead of every single attack.
This works great lorewise and classwise too since its short term buffing aura. Why wouldn't you want an aoe HoT added on to your big nuke that also increased the groups' dps?