PLEASE!!!!
separate occupation and annexion.
it means you can station troops in an other civ's city while not annexing it to your empire.
e.g. liberation: if you liberate your ally's city, she/he gets it back, however your troops can defend it against the enemy.

this idea should be elaborated but remember, annexions were usually made in peace conferences, not in the moment when the invader entered enemy territory.

please make it posible to station multi-civ forces in one tile!!!!!

Perhaps this could be an aspect of vassaldom?

THe difference between annexion and occupation were superbly rendered in Europa Universalis, and made for a much more realistic game, AND a better gameplay, AND a better immersion.

I say, put it in !