In the video, Bay suggests he is going to try to go "sideways" rather than bigger with more research into Transformers lore (and image of animated Unicron is shown). His desire is for something that isn't just action but something darker and more emotional. The video was likely recorded before he committed to getting TF3 out for summer 2011 and really its way to early to draw any definitive conclusions from the video as likely the film is still in the spitballing phase to see what sticks.
The video is below or click here which also has the solution to unlock the video. Thanks for Katie for the link.