I found some information on the new Dark Poeta instance that is coming in 1.5. From Fei of the Dark Avalanche Legion:
It’s a pretty big map ( ~same size as the lvl 10-20 area)
There are 16 Bosses, and you have to kill them in less than 4 hours. Heroic armors drop on these bosses, heroic weapons drop on the last boss. The last boss’ power depends on your score i.e if you reach the final boss pretty fast it will be stronger and it will drop some pretty good stuff. ( unfortunately we sucked and wiped 2 times, therefore we didn’t get the biggest boss (S grade is the best score.)
In addition he passed along these screens:
That’s it. You can find a couple of more screens and a thread on this topic here.