Whatever happened to it? It doesn't seem to exist. No matter how many players are in an area killing certain mobs, they always respawn at the same speed.
Like the elite orc area in Redridge, where the mobs still took 10 minutes to respawn, even with 15+ people in the area. Or the graveyard area in Duskwood with all the skeletons, still has really slow spawn rate despite 20+ people in the area killing them as soon as they respawn.