Bashiok does say that servers will take a bit to gain the momentum and general fluency with the encounters, but that it is entirely able to be pugged. Further, he says that from here on out, Blizzard has adopted the mantra of one cutting-edge tier, with the previous raids nerfed to allow players an easier time to complete them.
Personally, I am a huge fan of this type of content shift, and I think we've reached a pretty good compromise with regards to content accessibility and raid design. Raiders get their challenge while the content is relevant, hard modes are still skill-based encounters that do not get the nerf bat, and the previous tier of normal mode content is much more accessible to more casual raiders. Much as Ulduar drakes still presented a challenge in execution during Wrath even though we outgeared them, hard modes in Cataclysm are the execution challenges that will still prove to be tricky for meta achievements. Count me in.