I, for one, have absolutely no doubt that Arcane, as an entire spec, in both PvE and PvP is going to end up in the toilet throughout the entire MoP expansion. You can bookmark this post, screenshot it if you wish, but you will see that that statement of mine will stand the test of time.
I've never really seen mages as a healer class. As other people said it might make sense if you had it based around rewinding time and throwing out shields, but it still doesn't sit well with me. I made a mage to freeze people solid and then boil their insides before they can thaw. Mage tanking on the other hand is something I've always craved. The funny part is half the mechanics for a strong tank are already there. Shields? Check. Damage reducing stances? Check. AoE? Check. Just need a taunt and a spec that adds a buff to tanking stats with a nerf to damage.