The update is currently live for PC, PS4, and Xbox One, with the latter console receiving the 4K support for the high-end Xbox One X.
As for nerfs, both Mercy and Junkrat were hit with this new patch, though the changes to Mercy are the ones most players are talking about. With the latest nerf Mercy loses her bonus Resurrect charge through her Valkyrie ultimate, and Resurrect is no longer instantaneous. In addition, Valkyrie now only lasts 15 seconds (instead of 20) and her Guardian Angel ability is 50 percent less effective.
Junkrat's nerfs are minor by comparison with his Concussion Mine ability dealing less damage the further away an enemy is from the center of its explosion.
So yeah, 4K support on consoles is always nice but Mercy is pretty heavily nerfed in this most recent update. We'll probably have to update our Mercy Guide.