The bulk of the hour-long open Q&A session involved the current state of Japanese politics on the eve of the 70th anniversary of the end of World War Two -- and by Miyazaki-san's filmography, it is no surprise that he has many opinions on the subject. He did, however mention that he is taking three years (hopefully less) to tell the story of a caterpillar named Doro.
Miyazaki also indicated that there would be CGI involved, while Mark Schilling over at Variety is even reporting that the short will be made in 3D. However, it is unclear whether the short will be 100% rendered, or merely augmented with computer graphics, as Ghibli has done (often quite subtly) since 1997's Princess Mononoke.