The biggest mistake was to introduce personal housing in areas that should only be for FC housing. But the damage is done and I doubt much will change in that regard. LotR style housing with growing wards to accomodate the housing needs would be great but require a server investment on SE's side. Especially overpopulated servers like Balmung would easily go to 100+ wards in Mist alone.

Now, how to solve the problem? Make the Ishgardian housing simply better than the exsisting one. It needs to have better atmosphere and the appartments need to be bigger than the traditional housing. Make that is has standart, big and luxury appartments, with Luxury having several rooms, a big balcony and possibly a little instanced garden along with a chocobo parking lot. To get the neighborhood feeling, you could simply make it that a certain amount of appartments are on Ishgardian streets and that a new street is opened whenever the appartment limit on one has been reached. It would be a nice touch of things like items that you set on your windowstill could be visible from outside. Basically mini-wards that are not too data intense.

Appartments should also fully count as personal housing, meaning you can not have an abode in the Goblet and Ishgard, just to make exsisting plots less attractive in the overall picture.