Well, according to Drysc on the WoW.com forums, not very good. They have no plans to offer any more keys at this time, although they possibly will offer more beta passes in the future. If they do, it will likely be via contests or drawings on their own site, or possibly fan sites.
Not shocking news. From my own personal viewpoint, I am not that disappointed. Sure, I'd like to take the new car out for a spin before anyone else, but at the same time, I am looking forward to hitting the new content unspoiled with my guild.
Although don't take it the wrong way. I'd be MORE than happy to take a beta key off of Blizzard's hands.