I dont know if someone has propossed this before, but could make it so ward taxes apply dependin on the nation? Example:

Gridania: Woodcutters & Tanners Row be Free of taxes for this nation.

Ul'Dah: Jewelers, Chirurgeons, Masons & Clothiers Row be Free of taxes for this nation.

Limsa Lominsa: Grocers & Ironmongers Row be Free of taxes for this nation.

Battlecraft, Spellcraft, Field Craft, Tradescarf, Armortifiers, Crystaliers, Lower/Middle/Upper Tailors Ward remain unnafected and apply same taxes rules in any nation as how they do right now.

This way be a reason why to set Retainers in such areas and so people dont centralize in Ul'Dah.

Of course it implies the "free taxes" apply only for those nations instead the current peer row on all nations. But i think it would help set an order and balance and make people move their retainers from Ul'Dah wich would be main reason for this change.