Every World of Warcraft expansion has featured theme music based upon the same tune, from launch until now. The newest beta build for Legion includes an updated version of the title screen, but more important, it includes the newest incarnation of the login music. You can listen to it just below.
The patch contains other adjustments, of course, the usual set of balance patches and tweaks to existing talent choices, but you already knew that. You can check out all of the music that has been included thus far for Legion if you’re so inclined, or you can just hop on down and listen to the login tune.