According to this thread on the official forums, there is now an ability queue in WoW. To explain, currently if you push a button during a GCD, nothing happens because of the GCD. With this change, the first button you push during GCD becomes "locked" in queue; it is set to go off as the next skill you use. To some, that might sound cool: "I can decide what skill I'm going to use next earlier! That's awesome."
However, this leaves you unable to react to the ever-changing situation of combat. What happens when a proc goes off enabling/empowering Skill A, but you just queued Skill B? What if you notice you need to re-apply a DoT, but queued another nuke? What do you do in PVP if you queued up a damaging skill, but your target just got CC'd? The case of procs is where this probably hurts the most, as some procs (Bloodsurge) only give you a few seconds to react and the queue locks you out for another 1-1.5 seconds, giving you a smaller window in which to use your proc.
If this was an optional system that you could disable, I would have no problem with it. Some players (or even certain classes) could enable it if they found it beneficial, while others would not have to suffer unwanted changes to core gameplay mechanics. Hopefully Blizzard will add a toggle for this before it goes live.