Jane Jensen's new adventure game, Gray Matter, may have slipped to 2008, but she's still promoting the game and discussing the Gabriel Knight series in an interview with Gamespot UK.
GameSpot UK: Will there be a Gabriel Knight 4?
Jane Jensen: That's in the hands of Vivendi. I would like to do one, but the property belongs to them. So perhaps, someday, when they are ready to do one it will happen. I have two different stories ready for GK4.