Don't know. I believe it's going to be completely random though. Basically whenever The Korea Times finalizes something with the artists' respective companies, they'll announce them a few at a time.
Just as a comparison, last year they already announced their first batch of artists (including Girls' Generation) three days before tickets went on sale. Their second batch (well, artist) was announced mid February and their last one on the beginning of April.
Also, ticket prices were significantly cheaper too but depending on who's performing I doubt that really makes a difference.
I wouldn't count anyone out on showing up. From what I've read, people were counting SS501 on not being confirmed and they ended up performing last year. Personally I think if SS501 can go, KARA more than likely has a chance at performing.