Same here. Restarted client, restarted PC. I left it running overnight for 10+ hours, still Initializing…
SOLUTION: I ran the Wow.exe in my retail folder and logged in manually w/ authenticator. Once the game ran, the “Initializing” disappeared and the PLAY button lit up.
Hope this helps
EDIT: Looks like when you exit the game it goes back to Initializing… I guess the interim fix for now is to just run the exe and log in manually.