New content, whether it be a new expansion, or simply the Zul'Aman content, will be announced/revealed at Blizzcon.

So I opened up my email Friday evening to an interesting message from the BlizzCon people. The majority of the email was on information I already knew, where to pick up badges, etc. And then I hit the bombshell. They let me know that I will be able to copy my own character over to a test server in order to test new World of Warcraft content. This to me is the first major confirmation of what we already know: that a new expansion will be announced next Friday. Unless, of course, the only new content will be Zul'Aman, in which case Amanda will cry bitter, salty tears into her flat convention soda.