Nothing but necromancers
Thats because a lot of people want condi dmg in T4 fractals now. You even see LFGs with: 4 viper 1 druid.
I get the impression that you will see 5-scourge teams in PvP, too because they will need to be in the same group and move around like the Ant Hill Mob so they all have decent Barrier (i.e. to make up for the lack of Shroud), because it is super weak (at the time of writing).
Condi necro is incredibly easy to play but effective in a non-organised group.
Surrender and serve me in life, or die and slave for me in death.