The problem with current housing is some people make themselves illusions about some kind of show off "look how I'm rich" or keep a slot locked to deceive other players.
I'm not talking about people who actually use the houses but for all those who buy a plot and... that's all. No gardening, no workshop since it is for individual, no interiors creation... just a plot locked for nothing.
Adding wards or a tax will never solve this kind of problem. Delete the show off effect with upgradable apartments or instancied house and the data storage related to the wards problem will disappear by itself. Make housing a way that only players who really have use of it invest time and gils in it. That's why I really don't get SE's logic about neighborood or RMTs.
Instancied, shared with alts and one per world (let's says two : FC and individual) and solution done : no RMT problem, no data storage wasted. SE can't have a better control with this kind of approach.