Hope they'll do Firelands for the Cataclysm timewalking raid, it had some great bosses.
The reason for the achievement in Black temple was the limited choices demon hunters had for mogging their weapons. The devs said the achievement for themWas a one off and that future TW Raids would not have an achievement that made relevant legandaries moggable. People really need to read blue posts more often.
Blizzard should 2 timewalking WotLK raids, since it would be the only expansion with more raids dungeons. and I would have preferred the only 2 favorites, ICC and Ulduar.
Much as I would like to xmog Dragonwrath, Tarecgosa's Rest at some point, I do enjoy that bit of exclusivity left to legendaries (i.e. not being able to xmog them onto each and every toon).Val'Anyr was cool, but I don't want to see everyone running around with it.
There is no real point in doing the Ulduar timewalking unless you want to experience one of the best raids ever again, or if you are in need of 930/945 item level gear. It doesn't reward anything at the end like Black Temple did with the warglaive transmorgs for Demon Hunters, except Mimiron's Head which is probably the same drop chance as in the normal raid; 1%, and of course the Fragment of Val'anyr but the drop chance for those are low as well.