You could get away with 5 disc 5 ele shamans in LFR but your DPS would not be high enough for ultraxion, on deathwing's back parts of LFR. Maybe not even the final fight with Deathwing. You need a good steady 15k dps to be productive and Disc priests just cant do that and use PoH. There is a TON of AOE damage in fights and you wouldnt be able to keep up.