Adding fees to something that used to be free is a sure way to alienate your (existing and future) customers. Whether the idea of rent would be valid gil sink (or simply turn away more players from apartment ownership) is up to debate, but the timing for it is long past. If it were to be implemented with the current apartment system it’d need to be introduced back when apartment was first introduced.

Now if SE make it a rent for a new luxury apartment suite, there might be takers. Chances are they’d need to add balcony with view/cross-breeding capable flowerpots for it to actually appeal to the masses, but there might be player interested in paying rent even for a 2-floors or simply bigger apartments.

Dues probably isn’t that hard to implement. Simplest method they can just make you pay in order to enter your apartment suite.