They have said they will make an announcement before it goes live, as far as I'm aware. I would be surprised if it was any time soon.
It'll be sooner rather than later. Remember back in April, when LTC was scheduled to go live, MtGox was hit by both an unprecedented amount of new user registrations as well as numerous DDoS attacks, which pushed the release date. Since then they've addressed both issues, so it's just a matter of time before they pull the trigger.