The best solution is to add a small fee as an optional sub. The reason why this system has an issue is because of server limitations. Maybe basic it can go for free but you can have only one per account and if you want to have bigger then it must be a small fee per month which goes to keep up server cost.

The most important thing is that all players should be able to have housing otherwise it should be removed. Is no point in advising when you buy a game about the housing system or it must be more clear about getting a housing system before you buy the game.