Some of my suggestions may not be popular but I believe they would help.

-Create new ward maps with primarily medium and larges. Keep personal and FC wards separated.
-Make Flame/Serpent/Storm captain new requirement to get housing and to create a FC.
-Allow apartments to have different sizes. Allow gil compensation to people with ward houses that choose to relocate to an apartment. (I understand this could be abused, maybe a once per character/account thing.) I just know a lot of people would rather have apartment style medium/larges because they don't really care about yards.

And to give more incentive for people to move from congested to preferred worlds. Chocobo Feathers/ slight housing refunds/ and road to 80 or nice--but something that would really pull to preferred worlds.