Housing plots need rent. Sound horrible? Consider these facts:

[Yeldir]

As it has been correctly observed many times before, almost every server is speckled with houses associated with dead accounts that are not used, while active FC's and players are homeless. Failure to make payments would relinquish these plots for use by people who would actually be around to enjoy them.

EDIT: Krylo pointed out that, due to land changing hands as a result of nonpayment evictions, rent costs could be trivial, because buying the newly-emptied lots remains extremely expensive. Think rent costs lower than 5%. This, I think, is even better in practice and spirit than my own idea, because it removes inactive players, does not place undue burden on active players of modest means who fought tooth and claw for their home in the first place, and preserves the intended function of housing as a powerful, deflation-driving gil sink. However, controls on suggested advance payment systems would need to be very strict, to thwart the ease by which soon-to-be-inactive accounts could perpetually blockade paying customers from making use of the wasted lot.

Other good suggestions include, but are not limited to, non-payment of dues causing ward homes being forcibly moved to single home, server friendly instances, to preserve an expensive home while freeing a lot for more deserving players, ideally with the option of replacing the entire home with all of its goodies upon the purchase of a new lot. This would mean thriving, active neighborhoods, and a reduction in the devastating sense of loss felt by returning players who did not pay their dues for whatever reason. I believe FJerome, among others, advocate this idea.

Housing's secondary purpose is to destroy gil. This is an absolutely necessary function for the well being of this game's economy, and Housing has ceased to perform this function in any meaningful capacity. Aggressive rent prices as high as 5% or even 10% of a plot's cost a month, would turn Housing back into the gil vacuum it needs to be.

EDIT: "voclain im an economy major and aggressive deflation is bad, trickle-down economics works, richard nixon was not a crook and im not trying to keep my 8 houses forever, so we don't need gil sinks OK?"
Bad news. Your classes didn't cover fantasy dragon economies that exist in perpetual states of extreme inflation because every citizen therein can spontaneously generate unlimited currency by killing 8 rabbits for an elf. We do need aggressive deflationary measures to combat this, and the money best comes from the rich, as opposed to the poor, to lessen the gil-disparity between the two, and to make the tiny 800,000ish(?) gil allowance granted by completing the various quests in the world more relatively valuable, so new players have more relative purchasing power.

While you mansion owners would understandably regard such a system with horror and disgust, consider that most of you, like myself, are compulsive crafters who tend to accumulate outrageous proportions of our respective server's wealth - wealth that needs to be continually destroyed to protect new players from being thrown into the deep end of an economy that absolutely will drown them.

A few of you might remember Dark Age of Camelot's housing worked on exactly this premise. You could fit a limited amount of platinum/gold in your home's drop box, to allow you to step away from the game for several months, but you had to play and make your dues, or your plot would be repossessed (your furniture and goodies thankfully stored safely on an npc who would return them to you in the event of repossession) and your plot given to someone who deserved to have it better than you did.

The system worked very well, and it would work well here, too - pay up to three months in advance, or even have your friends pay in your absence. Just as long as if you quit, you lose your home. Of course you should lose it. The present system is completely unfair to new players.