Oh Housing! A possible solution for the future.
I don't know the future. I don't know what Yoshida and the devs have planned to fix this personal housing debacle. What I do know is that based on what they have already done, this model isn't sustainable for more than 2-5% of the active population. So based on what we already know about how housing works my very much band-aid solution is this:
Analyze the population and gil totals per server, and add more wards to the higher pop servers with more wealth.
If a legacy server has 20,000 active accounts, and a non-legacy server has 4000, then give more housing wards to the legacy server.
This will do a few things: It will enable the higher pop servers to have fewer people left out of housing. It will enable you to extract more gil from circulation. It will do more to prevent wards from being ghost towns on small servers. And most of all, it will enable you to purchase the physical servers in the most cost effective manner.
Giving square the benefit of the doubt (lol), they have probably considered this and it can't be done for one reason or another. But on the very slight chance that this option wasn't considered, I wanted to throw it out there.
This system is far from perfect, but I think that adaptive allocation of wards based on population is a much better solution than every world gets the same wards across the board.