A few theories, but this fan has good pointers.

1. Zim reruns return for a month, and its heavily promoted.
2. A new Zim game is added to Nick.com
3. The Zim DVDs are re-released at an expensive price of $50 for all 27 episodes
4. And the biggest clue of all...this Nick.com message board thread started by a moderator of the board.

Link


Also let's not forget Invadercon, featuring "Dinner of Doom" and an entire month of Invader Zim facts from Johnen Vasquez.

I edited this news post to include a working link ~TheDarksage