Let's see... an updated Merchant Prince, maybe expanded enough to be a full-sized hardback - I don't know if anyone wants to tackle a boxed set on this.
Perhaps politics, covering not only the Third Imperium but also the Zhodani, the Solomani, and possibly the Hivers. This one could easily grow into a boxed set, especially if you start covering the interactions between these groups... and include their interactions with Vargr and Aslan politics, as well. Shoot, just the interactions between the Imperium and the Zhodani would basically be a lead-in the the Fifth Frontier War, which gives you some idea for the potential scope of such a megaproject.
Rules on technology development, and how characters can participate and even drive things. This could also tie into economic development, as well: how does a world go from a fledgling colony to an industrialized hub of interstellar trade and learning? How would an aspiring leader - or grand puppet-master operating behind the throne - cause this development to happen?