Missions that allow you to upgrade your apartment.
Like the "homestead" missions from AC.
Or you could purchase upgrades from an in game website, similar to how you can choose upgrades for properties in Skyrim.
Steal elements from The Sims when it comes to placement of items in your apartment.
It'd be awesome to see what your mates do to their apartments...It'd actually give you a reason to visit them, instead of looking at an exact copy of your apartment.
Like having snapomatic picture frames on the wall.
Being able to invite your crew over to play pool or poker.
Would love to be able to put my stamp on my own place, even if it's just to select features that you can alter.