Google's specially good at launching those "beta" concepts which look so cool but might have some issues at the very moment of launch. People are used to things that "look cool even if they only barely work" because they know that, later on, Google will improve them.
I'm sure that Facebook can pull off the same thing. And, in that regard, we might not need an interactive "FaceWorld" with "millions of avatars" on Day One. If they get "thousands of avatars" listening in on a live concert, that would be awesome enough.