All they needed to do:
1-Add customizable instanced rooms. (Like the currently useless inn rooms)
2-Add public Chocobo stables in cities and housing wards.
3-Add flower puts to use inside the rooms to garden in.
4-Make Room free in your starting city, and paying some fee to access it from other cities.
...
TLDR: Mog Houses. All the needed to do was copy mog houses from XI.