Balconies would be lovely.
As many people before me have mentioned, I would also love to see the ability to buy or quest extra additions to your house. Perhaps themed rooms (like a mount stable or crafting room).
My dream would be an instanced house wherein you may invite friends into. How big or many rooms is an extension of your player status. With playstion Home style furnishings made obtainable by participating in events and quests in game.
Some other furnishing crafted too.
I don't know if its techincally feasible or not, but would be nice if you could purchase new skins for walls/flooring so you can theme a barren room to your specific tastes. Such as placing a tatami mat floor if you're feeling traditional, or dungeon walls if you're in a dark mood.
I just really don't want to be crammed into a studio basement apartment as I was in Bastok back in the day.
After saving the world a few times over the course of the game, my character should at least have earned something resembling a house. ^^;