Priests should get Holy Form instead of Lightwell. How cool would that be? Instead of dark see-through shadowly look with Shadowform, Holy Form would give us an aura of light, which makes us glow.
32% of base mana
1.5 sec cooldown
Assume a Holy Form, increasing your healing spells by 15%. Increases Physical damage done to you by 15% but reduces threat generated by your healing spells by 30%. However, you may not cast Shadow spells while in this form. Stamina is reduced by 50%, but Spirit is increased by 50%. Removing Holy Form gives you a Burned Soul debuff for 15 seconds. During this time, Physical damage done to you is increased by 30%. Burned Soul is undispellable, but will be removed when Holy Form is reapplied.
Overpowered in PvE? Maybe. But we need something to replace Lightwell. This will give us an immense boost in healing, which we perhaps don't need, because in PvE, Priests are doing fine, *cough* except for the mana issues *cough*. This skill would be crappy in PvP, though, because of the stamina reduction and the increase in damage taken. So overpowered in PvP? Nah, because if people want to remove it, it would be a bad move. The Burned Soul effect (much like Weakened Soul) will prevent people from removing Holy Form in PvP, to bypass the stamina reduction and the increase of Physical damage done to the Priest.
Shadow has got a form. Why doesn't Holy? Give the Priest some love. We will love little boys in return. Hell, even Druids have a form to increase healing. ^^