Considering that Dragon Soul was obviously a very late decision by Blizzard caused by them scrapping War of the Ancients raid, the Deathwing raid could be much better, and probably use more new content and models. How do you think it could play out?
I imagine that the Deathwing raid could be set deeper in the Grim Batol, using dwarven architecture but corrupted and Old God-esque, all purple and orange - starting out fairly deep but eventually ascending until we finally face Deathwing at the very top of his fortress. Alternatively, he could have taken Wyrmrest, warping its architecture and expanding its underground chambers.
Bosses would include dragons, elementals, Faceless and Twilights, each having their own wing, so that the raid would be nonlinear, ending with Spine and Madness, and probably his human form before that. However, Deathwing would appear earlier as well, threatening us and aiding bosses.
And no Thrall. NO. THRALL.