How about adding traps that local lords can purchase for their regions from siege workshops? Falling rocks, boiling oil, catapults, ballista, etc. You can even make current seige options scaleable. For example, an infantry unit can purchase a battering ram and later upgrade that into a siege tower. Archers can purchase ballista, MI can get catapults which can then be upgraded to trebuchets. All of which stays with your current unit as siege weapons currently do so if your unit is lost then you loose your investment as well.
we got options, y'all.
