I don't think they could make things much shorter. Currently there are four raids out; Naxx, Malygos, Sarpharion, Archadeon. Naxx is built like karazahn in the sense of there is trash then boss trash then boss. The other three however are basic zone in's and you're at the boss, much like Onyxia, and Magtheridon. Heroic Occy is currently the longest instance, I've heard stories of it lasting as long as two hours, it is also said to be the hardest isntance, next to HoL.