According to this latest bit, Fantasy Flight is working on a game dealing with the Great Crusade. Although there is little to no information on this, I am a big fan of Fantasy Flight Games and look forward to seeing what they come up with.
Please remember that this is a rumor.
via an anonymous source on Faeit 212
By the way:
Fantasy Flight Games working on a new "40k" game with the great crusade / horus herey timeline. No details at the moment.