The easiest way this would work imo is that you get a choice prior to the new housing plots opening if you want to move or not. If you want to move you are queued up to automaticly move the house under the maintenance before the plots open, but you don't get to choose where your house ends up. If you own, let's say Plot 16, you move to plot 16 in the new area. If that plot isn't in a location you truely wished for you have to sell your old house and move in manually.