Don't get your hopes too up, I can't find the source either
It might have been a small mention at Blizzcon or in a dev twitter response, but it could also just be me misinterpreting something or even wishful thinking xD
Edit: They did make a mention of it in an interview, although it's not quite what I wish for, there's hope:
Originally Posted by Blizzard Entertainment
Ion Hazzikostas: One thing I will say in general about lessons learned from Warlords of Draenor in terms of the storytelling, the level of an experience is not in question. We had a very clear compelling powerful story. In our raids and dungeons we kind of touched on where that story ended up. In terms of bridging the gap between those while we were telling that story, it was often in a way that felt disconnected from the world itself. Kind of fragmented. We’re really trying to much better integrate that storytelling in game so there’s a clear plotline that players can follow from start to finish.
Tom Chilton: We definitely want express it more through the max level content than we did in Warlords.
source