I think this change was hastily implemented, considering we can't "see" mobs standing directly in front of us a lot of the time.
Some of you are misunderstanding the change.; The only change to the /target command is that it now checks line of sight to make sure the mob isn't behind a wall or in the next room.; This has nothing to do with the rendering issue and mobs rendering late.; You'll still be able to use it to target a mob if he hasn't been fully loaded on your client yet.
There were just way too many situations where people could exploit by pulling mobs through floors, through rooms where you hadn't yet unlocked a door to get in it, etc.; In no way was this a change to 'nerf' anyone.