A post from Blizzard to the Diablo III forums discusses Greater Rift damage scaling, saying they are looking to create a "more consistent" Greater Rift experience in the action/RPG sequel. Word is they are planning to disable the ability for some characters to have 100% crowd control uptime as part of this:

Hey guys! Just wanted to say thanks for taking the time to give us your feedback about scaling damage in Greater Rifts. One of the key goals of Greater Rifts is that they serve as a form of measuring stick for a characters power growth, and we feel that scaling damage is a very important element of their ability to function in this way. That said, we’re currently looking at our options for some possible adjustments to how this damage scales in the future.

We’re looking to disable permanent Crowd Control in an upcoming content patch to create more interaction with monsters at higher Greater Rifts levels. To complement that change, we will be also be evaluating how much damage monsters are dealing to players in that environment. One of our goals in the next major patch is to provide a more consistent Greater Rift experience while making sure that defensive Legendary items still matter.