When I was there in August, I was chatting with a CM at Tatooine Traders and he was claiming that it is already in the works for 2004. The dates were not oficially posted until mid February last year and the people were not announced until March.
One thing to note is that in 2002 there was the release of Episode II, which took a lot of the time of the actors and creators. This year, we caught the actors just before they had to go to Australia to start filming Episode III. I don't know if that would affect the people who would possibly show up for the weekends.
I would start checking around late January/early February in hopes of getting dates. I am hoping for early May so that I can get a fourth trip into this AP.
You can also check with Guest Services at MGM to see if they know anything about dates or have some sort of rough schedule that they can provide.