Well I cannot remember which interview because I watched several of them over the past few days…one with Ion and two others with Omar.
But here’s a link to the EU forums. That first post has links to all the interviews.
(sorry for the mess…I cannot post links)
eu(dot)forums(dot)blizzard(dot)com/en/wow/t/whats-layering-heres-what-the-devs-say/51848