Might to want to clarify that they wouldn't be reselling the house for gil after purchase in an auction system. They would be selling it for real money. If you've outbid the gil other interested buyers have, there's no one left to sell to that would result in a gil profit.
The solution exists and others game use it - a fully instanced system that allows every character (not just every player) to have at least one and frequently multiple houses. No player who wants housing gets left out.
Why SE won't use something proven to work in other games and make their players happy is something only SE can answer. We know they like the idea of neighborhoods but in practice they don't work out. They didn't stop to think what makes real world neighborhoods feel active and populated then incorporate those things into the wards to keep them busy.
Wards don't feel like neighborhoods. They feel like abandoned towns. I'd be happier living in an isolated part of the countryside than living in a suburb where no one else goes.