One of the more talked about changes in Phase 3 so far has been heavy nerf Soul Link received. The spell will no longer work in conjunction with Metamorphosis.
While this is a hefty nerf for some tanks in PvE, a lot of Warlock tanks preferred to play a more offensive Destruction tanking build.
For tanking this change seems to be the opposite of the Shaman tank nerfs that came with Phase 3, who received a significant hit to their damage and threat instead.
To view all Datamined Class Changes in Phase 3 Season of Discovery, check out our news article here.
Cannot be used while Metamorphosis is active
On the other hand, this is a big change for PvP performance, as combining the two in PvP lead to one of the bulkiest characters in the game, able to start and win the war of attrition every time. I'm sure the brains behind Warlock theorycrafting are already cooking up something special to replace it.