Though achieving permanent invulnerability in Diablo III has theoretically been possible for a while through hoarding cooldown reduction items, this has been a difficult process which has resulted in suboptimal builds. As new items make this more possible all the time, a Blizzard community manager reveals that by changing with way cooldowns work, they will make it impossible to chain immunity skills endlessly, as cooldown timers will now begin after the effect ends, rather than when the skill is triggered. On a related subject, another post says they recognize the circus of icons constantly appearing and disappearing from player's screens is confusing at best, and they are looking at clearing this up. Word is: "That said, we’re currently reviewing how we display buffs and cooldowns, and looking for ways to ensure this information remains easy to access and interpret quickly, so you can stay focused on the game." Here's word on how they are changing cooldown reduction:

Starting in the next PTR patch, we’ll be applying this philosophy to the following immunity skills.

• Spirit Walk
• Serenity
• Smoke Screen
• Laws of Hope – Stop Time

With this, the cooldowns on these skills will begin after their buff ends. To minimize negatively impacting the normal use case for these skills, we’re lowering the cooldown time to compensate – for example, Serenity is going from a 20 second cooldown that starts on activation, to a 16 second cooldown that starts when Serenity ends.

Previously, we may have decided against adding an item power to the game that might lead to permanent invulnerability. However, with these new changes, we’ll have much more freedom in designing new and powerful items, since there will be a stop gap to ensure that permanent invincibility is no longer a concern.