They are making it so you can no longer simply Teleport through walls to the bosses, I.E. nothing like Diablo 2's 66 second Ancient Tunnel's runs. Preventing people from farming bosses is not possible, at least I don't think it is. All you have to do is create a game, kill boss, leave game, create new game etc. I fail to see how they could regulate that.
OT; I am looking forward to finally having a Time Sink, I have long been gone from WoW & I can't stand console gaming for much longer. It will be nice to have a new game, with new objectives. Though I am mostly looking forward to not having these cookie cutter classes that we had in Diablo2 (Hammerdins, Trapsin etc.). It is looking much more technical, which I love. Can not wait to finally play my Barbarian