So this thread is a work in progress, since these require rep and we need devs to spawn them. There are two new raid rifts. The difficulty is supposed to be par with Hammerknell 20man and require similar stats to take them down.
I was doing a story quest when I ran into a Fire rift, but the NPC's has 268,000! health. It looks like first phase is 3 pulls of three adds each with 286k health and mostly physical damage.