Not sure when and where this was held, or why, but this was a media event with Voice Actors and Writers, for the release of the DVD/BD.

http://tformers.com/article.php?sid=12456


POSSIBLE SPOILER:

From the article, there looks to be an easter egg in the BluRay release that has Michael Bay suggesting that Unicron could be an element in TF3.

Considering all the red herrings he gave out for TF2 (like saying that Megatron was not going to be in it), this is a rumour that shouldn't be taken seriously until we see it on screen.