The way they described it on the podcast as I recall was basically, 'The WoW client handles a lot of things really well. It's known for being very responsive. When you use an ability, it goes off right away. We have some technology we're working on that should make it even better.' and then one of the people on the Convert to Raid podcast asked if it would be something we would see mentioned in the patch notes or explained, and they said something along the lines of, 'It wouldn't really be something mentioned in the patch notes, as it's not a new feature. Maybe something like, "The game will be even more responsive now."'
This is just me paraphrasing off of memory, but it sounds interesting. Right now it is quite rare that I use an ability and it doesn't go off right away. But they cited some rare situations where an ability is used, its cooldown is triggered, but nothing actually happens - and whatever change they talked about would help ensure that that happens even less often/never happens at all.