At the moment we have the following categories of CC:
Disorient
Incapacitate
Root
Silence
Stun
Knockback
Where only abilities listed in each given category share diminishing returns (basically meaning that you can be CC'd indefinitely as long the CC is coming from a different category each time)
For me this is one of the biggest problems with PvP in WoW. Blizz tried to address it pre-WoD but lets face it, any attempt at improving PvP from Blizzard is always half-assed.
So here's my solution. Create 2 categories of CC:
1. Any ability that removes complete control of a character
2. Everything else.
So basically you'll be merging ALL Disorients, Incapacitates and Stuns into 1 branch where every ability that acts as one of those 3 forms of CC will share the same diminishing returns.
On the other hand you'll have ALL Roots, Silence/interrupts & Knockbacks sharing the same Diminishing Returns.
Now for those thinking that a change like this would make it far too easy for say healers to just dictate play on their terms because they can no longer be "chain CC'd" I would say one thing. "Make mana relevant" If mana can go back to actually being important and not just a pretty blue bar that sits under the green one then healers wont be so powerful and won't be able to spam heals for 15mins in an arena game (this is starting to steer away from the topic) but don't think that this would make PvP worse. The stage where it's at now where a mage can stand there and just spam polymorph 5 times until the other person becomes immune to it is really stupid and needs to stop.