I had the same black screen problem on my Macbook Pro so I downloaded the client from a different link which then just gave me an error message whenever I tried to open the game.
From researching the black screen might have something to do with the screen resolution but my error message seemed to be a problem with wow.app.
The way I got around it was lowering my screen resolution and then to ctrl click wow.app and select Show Package Contents and in the Mac OS folder open the wow Unix Executable file. It opens terminal initially but then loads the game which worked.
I know it's a faff but it got it working. Hope it helps!
