The sun domain would be a good be a fit. Like some classes that borrow from others, the Priest version of turn undead might come with an asterisk such that "Uses of turn undead gained from the Priest class may not be used to power divine feats". Another thought is you could grant it at the lesser stage and from that point on advance it as a Paladin would, weakening it slightly from a full powered cleric. Perhaps both of these.
Sun domain is getting a new ability, due to Turn Undead not being accessible by Priests. It'll probably be something similar to 'any light spell cast becomes true daylight for the purposes of affecting certain undead'. This gives them a powerful weapon to use against undead, particularly vampires and incorporeal undead, without being able to be used for Divine Metacheese.
Originally Posted by The Underlord
All hail great Shneekeythulhu! Ia Ia Shneeky fthagn