Aint It Cool News published this report based on an article in Newtype Magazine. The interview is with David Carradine:

“Bill wouldn’t be in the sequels,” said Carradine. “The original concept calls for two sequels, but they’re going to be shot quite a bit apart. The children of some of the characters in this pictuire will become the stars of the subsequent movies, but there are also plans for a prequel that would be animated. It would be done with anime, as far as I know. That would take you back and give some of [The Bride’s] backstory.” “As far as the prequel cartoon and, to a lesser extent, the sequels, these are visons that Tarantino has...”