How about if they made the house watcher npc guy tell you the total number of plots currently available on the datacenter and which worlds they are on. Then if you visit the world with vacant plots and buy one, it automatically changes your home world to that world and waives the transfer fee. And the transaction fails if you have some condition that would prevent you changing home world.

That way the blame can be shifted to the players for staying on a congested world while the npc is telling you houses are readily available elsewhere. And if the entire datacenter is full I guess people just need to share with tenancy and fc estates. Promote the feature with a campaign period, receive gold feather or something for performing some sort of action as a tenant of a friend's plot.