Edit: Never mind about the thread. I just realized that the key talents are in Arcane tree, and then this can becomes a variation of Arcane-Frost build.
From quick browse through the Armory, I see a lot of priests with their normal regen close to 500mp5. It seems to me like they are not giving up too much SP either--although they are not going to be nearly as crit heavy (or haste heavy) as Mage.
So I was wondering if Pyromaniac and Arcane Meditation stack? (Both say it lets you regen 50% mana while casting. This should push you up to 100% regen during 5sec rule)
Combined with Imp Blink, Arcane Shielding, and Prismatic Cloak, and you can still grab Dragon's Breath in the Fire tree. Then you should be able to put up the shield, go for a quick AoE run, Blink out (or for coolest effect, Blink in, blow your AoEs, then use Invisibility on your way out), or use Dragon's Breath or Blast Wave to give yourself some distance, take the time to regen (while waiting for cooldown), rinse, repeat. Hopefully you'll have procced Hot Streak for a quick Pyroblast finisher. The extra Spi should boost your crit quite a lot with Molten Armor as well.
So.. would this work, or will I die a painful death like all fire mages who decided to PvP?