Parece ser que ya está disponible el cliente en 64b para World of Warcraft.
A 64-bit client is once again available for use with Patch 4.3.2. Before being able to launch WoW in 64-bit mode you will need to download the 64-bit client for PC/Mac (using one of the links below), and unzip it into your World of Warcraft directory. Once you extract the files you can start the 64-bit client by opening the Launcher as normal (Run as Administrator if applicable). To switch back to the 32-bit client, go into Options -> Game Preferences, and check the Launch 32-bit client setting. The game will display which version you are using at the bottom left hand corner of the login screen. ex: Version 4.3.2 (15211) (Release x64)
Important things to keep in mind
The 64-bit client is being distributed separately from the Retail version as it is not yet supported for use with World of Warcraft.
Launching the game in 64-bit mode can only be done after patching the game to version 4.3.2, downloading and extracting the necessary files.
The games built in voice chat does not currently work when using the 64-bit client.
[Mac] The 64-bit Mac client does not currently support the in-game movie recording functionality.
[Mac] The 64-bit Mac client iTunes' Remote feature does not work at the present time.
[Mac] The 64-bit Mac client does not currently support the customized LCD display for the Logitech G15 series of keyboards.
[Mac] The 64-bit Mac client is currently not supported on 10.5 systems. You will need 10.6.8 or later for this version.
Additional System Requirements:
Windows XP Professional x64 Edition / 64-bit Windows Vista / 64-bit Windows 7 (latest service packs).Mac OS 10.6.8 or newer.Mac Computer with Core 2 Duo or better2 GB or more of RAM.
If you encounter any issues while using the 64-bit version, please report your findings in this thread and return to using the 32-bit executable. In order to facilitate support when contacting Technical Support, please inform them if you are using the 64 bit client.
To remove the 64-bit client completely, delete the following files from your World of Warcraft folder:
World of Warcraft-64.app
Ya está funcionando para los servers europeos. En el hilo oficial están los enlaces de descarga.