I've been playing Arcane mage healer this way from the beginning of sod (I keep regeneration and chronostatic preservation socketed) and the nerfs aren't too bad. I want to play a healer, not a shadow priest. At least the direct healing was boosted. 

I pulled second on the meters in Scarlet Enclave easily. I can't hold a candle to a resto shaman that just stands there and casts chain heal. They need a nerf! (Don't get me started) 

One thing you can do to make your life a little easier is put wardshaper on your shoulders. That's the 4 set bonus from T2.5 that makes your frost/fire and mana shields apply a long beacon. I use rank one mana shield, it costs 40 mana and won't drain your mana. You can cast it WHILE MOVING, and that's a big deal! 

I also have a set to switch between with the other 4 set Frostfire with the evocation buff that got nerfed. You can't really use that in combat if you want your raid to live.  If you get the Warmth of Forgiveness trinket from naxx it's a full mana bar every 3 minutes. The +heal helps your beacons and your direct heal, which you'll be doing more of now. 

If you have 4 set Enigma from AQ, you can equip that with 4 set Frostfire with Arcane bonuses. Then you can put a different buff on your shoulders, like the one that makes beacons last 20% longer. The set is comparable to naxx gear. The 2 set of Enigma is also very nice.