Well my take on pretty much all of the UI changes is this :
(1) The less work an addon author has to do the better
(2) The less code an addon author has to support & debug the better
(3) If the feature provided in the built in addon is adequate enough then the code to provide such feature already in an addon should safely be taken out. Benefits are as (1) & (2) above.
Blizzard's pretty much always done this IMHO. Just look at the raid frames. RDX & CT Mod had those first.
IMHO It's an honor when Blizzard implement a feature from a third party addon in game. Sucks that they don't acknowledge but still an honor in my eyes
