Might as well sell your plot now (If its a private estate only) and get some Gil for it, as when you go to purchase a new plot once the move feature has been added (Companies only for the moment) you must pay for the new plot just the same as if you went to a placard right now to buy a plot. You will not be refunded for your current plot unless, you wait 45 days without entering it and then get refunded 80% of the purchased price, or on-sell it to another player.