I'd like to see the door lead to my own *personal house* honestly - like:
(For those who havent seen the movie, its Howl's Moving Castle and the door lets you turn the dial and walk through the door to different locations (top right - each color represents a different location and the needle is the current linked location))
Otherwise maybe just have a living quarters where its a bunch of bunkbeds and chests like a barracks.
* (If you dont own a personal house then perhaps the FC has a basic room supplied to those who dont own a house - can maybe do some personalizing to the borrowed room but not on the cost or scale as a personal house)
The door linking would be specially useful if your FC is in a different zone then your personal hosue - just turn the dial and walk through. Could even make the zoning seamless (close door, turn dial, game: unload current zone but not your inside house, game: load FC zone, walk through (door closes), game: unload house (unless your computer can handle the extra memory in zone), never have to go through a loading screen).