Ishgard won't be out for a while so don't get hopes up soon. They still are working on the house transfer system as well that they mentioned since they want that for Ishgard housing release so players who own houses in the other wards if they go buy a plot in Ishgard they can transfer their house and everything with it to the new ward. The current housing situation is this; Demolition of houses that are unoccupied/unused by people who have gone inactive/quit for over 45 days. If the house is not entered by the owner / FC member(s) (let's remind people there are lots of single player FC's owned by alts of people who may have quit). Then the house is demolished and put back up on market for first come first serve basis.
However we know that's not going to help alleviate the issue of the mass demand for houses that the player base wants. Hence where personal house sharing comes into play. Many people who are married in the game wanted a house to share together. Others who had personal houses wanted to share theirs with friends. Now you can share a personal house with up to 3 other people. Making it 4 players per personal house. This may also be a hope on SE's part in helping to resolve housing issue. Now let's say a married couple both own personal houses, now they can live together in 1 house. If they aren't greedy/selfish then that will open up one plot. Those who do not have a personal house and are good friends with others. Now you can have a house to share with up to 3 close friends and they can have access to all the things like decorating, garden, and such. It's like having a roommate irl. So even tho it's not your own personal house you now have a house you share with a few people making it easier to let everyone do things instead of with a huge FC where there's way too many people and restrictions are set in place for reasons. Also maybe friends want to share houses together but each one owns their own house. They could as well figure out which one of the houses they want to keep to share and then give up the other. This way SE can see within a few months how much housing has opened up from this system. How many people are sharing houses and how many wards to add on when they bring in the next housing update with Ishgard.
More or less it's about seeing how the community will act. Will married couples who own 2 houses each move into 1 shared house and free up a house? Will friends that all own houses either give up their house and move in with a friend? Or will they invite and share a house making it a personal house for 4 people. It's an experiment that really relies on the community, but this will be good info for SE to know what to do for the next segment regarding housing issue.