Well if it will get nerfed i dont know of course but a fact is still that even if you have the 1100 +dmg you will still be chainpotting mana potions, making shadowpriests sill the most consumable dependant "DPS class".
Example: On an avarage magtheridon kill i pop about 3-4 mana pots and i am able to use my shadowfiend 3 times. now after some time i watched a movie from a mage on magtheridon. The optimal mana preservation (without popping pots) would have been using his evocation at the start of the fight (75% mana?) and then be able to use it again near the end of the fight. but the mage actually didnt do this but only used his evo Once in the fight making him near oom near the end of the fight so he had to pop a mana potion. For me not popping a mana potion in this fight would make me oom around 50% i think and i have 1000 spelldmg unbuffed on this magtheridon kill it would have been a lil higher since i had raidbuffs obviously.
The fact is that with the dmg nerf shadowpriests have we cant do optimal dmg anymore unless we can use the optimall cycle in which you can include SW

and MB. well if i use this cycle for more then 3 minutes without any mana regens (except normal raidbuffs and wisdom) i would be oom.
Untill the optimal DPS cycle would be allmost free of mana and shadowpriests get free of the usage of mana potions i dont think the mana regen should be nerfed. Not to forget that this is what makes shadowpriests actually needed in raids.
I havent played WoW to long before the burning crusade but i do know that raiding shadowpriests were rare in those days. Why? because they were not mana efficient enough. Blizzard fixed this with VT and Shadowfiend and gave shadowpriests an important raid position if they start nerfing these abilities again i doubt how long it will take before lots of priests will spec back to Holy for raiding (and we cant say holy priests are very powerfull in raids atm :P)
I am not an expert so correct me if i am wrong on many of these points but this is my vision on how shadowpriests currently work in raids.