I'd still have an enemy similar to the Brood. A hostile alien race on the frontier the Empire wars against. A few light years out from the frontier is the occupied and smoking remains of the Brood Home World, with the enemy empire still controlling a hundred solar systems. Far to small to ever defeat the empire, but a great adventure hook. Primarily I could see a real xenophobic fervor sweeping the empire, with Emperor all to eager to promote humanistic patriotism, so easily channeled into faithful vassals.