In 5.2 the changes for disc priests simply remove the faceroll aspect of the spec which is cast prayer of healing till you smash your keyboard even if its 100% overheal but that doesn't matter cause rapture gives you infinite mana plus the only thing you care is getting divine aegis on every single person asap, add spirit shell to the mix and you have current disc priests. This strategy right now is stupidly effective and promotes facerolling to the maximum so inevitably it gets hit with the nerfbat to weed out all the fotm disc priests that will jump ship the moment they ain't overpowered anymore which is a similar situation monks were in before 5.1 and bring some well needed balance to healing.
In addition in 5.2 the strengths of each spec and emphasized correctly in regards to priests.
Want better healing output spec holy, want absorbs spec disc. The price you pay for speccing discipline is inferior healing output but you get absorbs instead, in other words you can't have your cake and eat it as well like you do now while being discipline which allows you to have the best of both.
Finally the sky is not falling like your implying in this thread it will because you haven't even tested how these changes actually affect disc in a 25-man environment because guess what no 25-man has been tested yet only a bunch of 10-mans and disc is perfectly fine on those after said nerfs.