Kil'Jeaden's Cunning change.

Kil'jaeden's Cunning felt too good. Most Affliction Warlocks were taking it. The developers weren't too happy with the snare effect, but not many warlocks were using it when it had a cast time debuff. Changing KJC to a snare effect ended up making the talent too attractive. There's a long PTR cycle ahead of us, and the developers will have plenty of time to adjust it. You can also rest assured that Warlocks will be balanced around it.
It's worth noting that the new Kil'jaeden's Cunning is off the global cooldown and can be cast even if another spell is already being cast at the moment.

One recent change the developers have made in the 5.4 PTR is that Haunt can now be cast while moving. They will also discuss Fel Flame's interaction with DoTs, although they worry it might to get it in the right place.

Edit: Typo fixed!

Although some of you have mentioned it already, there're a few updates from the developers that we wanted you to know. This is in early testing and subject to change.

Fel Flame has been slightly reworked. Now it has a 1.5 second cast time, but can be cast while moving. It no longer extends the duration of damage over time effects and has received a small damage buff. The intent is that you'll use it to keep up some damage when you need to move, but you'll want to stick to your standard rotation otherwise.

For Affliction specifically, the developers are lowering the bonus damage that Malefic Grasp provides and moving it into Haunt and the DoT effects themselves to compensate. They still want Malefic Grasp to be your primary filler for single target DPS, but this will make it a bit less punishing when you can't afford to channel it (especially in PvP). Haunt will once again be interrupted by movement, in favor of the Fel Flame change.

Kil'Jaeden's Cunning and Mannoroth's Fury have had their cooldowns and durations lowered to 60 and 10 seconds, respectively. Mannoroth's Fury now only applies to the core AoE damage spells (Seed of Corruption, Hellfire, Immolation Aura, and Rain of Fire), but increases their damage by 100% while active in addition to the range increase. Rain of Fire is being changed to no longer generate enough Burning Embers to be worth using in a single target rotation (so, Destruction shouldn't feel forced into Mannoroth's Fury).

These changes will be available on the PTR with the next build. Please remember that we're very early in the 5.4 development process, and therefore any or all of this may still change before the release of the patch.

As mentioned by Glan, we recently posted some new information regarding the changes to Kil'Jaeden's Cunning. Thanks for all of your feedback on this topic so far and we hope to see even more as we continue to make further changes to the PTR.

Just to highlight the post that was quoted by Glan:

We've been following all of your feedback very closely, and we're going to try a different approach to Kil'Jaeden's Cunning in 5.4.

In a future PTR build, Kil'Jaeden's Cunning will once again be a passive effect. Selecting it will allow the Warlock to cast Malefic Grasp, Shadow Bolt, and Incinerate while moving. There is no penalty, so you'll be able to move at full speed.

We still feel that the 5.3 version of Kil'Jaeden's Cunning isn't working out, but we don't want to "nerf fun" either. It's clear that many Warlocks simply enjoy the feel of being able to cast on the move, and we'd like to be able to preserve as much of that feeling if possible.

With this change, we can make the "penalty" of taking KJC that you don't have Mannoroth's Fury or Archimonde's Vengeance, which should result in more damage output in cases where movement is less critical (and we're working on some changes to Archimonde's Vengeance that should help with that). We're also still planning on buffing Fel Flame in a way that helps lower the impact to mobility caused by choosing one of those talents over Kil'Jaeden's Cunning, without nerfing it for PvP purposes.

Remember, we're still extremely early in the PTR process. There will be many more changes to the game before the patch goes live.