I think it would be a neat feature if one did not have to take a whole city in 1 siege assault. It would be great if you could take parts of the city in siege assaults and be able to hold them for more turns.
Say you could take the first two rings of a city in one siege assault. Then wait a few turns for reinforcements and then go on to take the inner citadel, for example.
To add to this one could build their own make-shift defenses such as trenches/walls/camps within their captured area in case of the enemy sallying forth. - If this is too much then at least being able to build trenches/walls/camps outside the city when you are sieging would satisfy.
This would do great for the immersion in my opinion.
Those of you who have a high degree of knowledge in Japanese history - did such things happen? or were the taking of cities usually done in one single assault?
Evan