If ever I decide to transfer and level my priest, I may go this route and Level a Priest / Warlock / Mage in style. Here’s a list of heirloom items.
I would probably get the cloth set first as it can be used by any class. It might not be optimal, but it would probably be better than a lot of the early level gear even for leather/mail/plate wearers. I’d have to play with the numbers to confirm this. It would also push all classes with mana to a caster style of play which might defeat the point of rolling a new class.