Why can't players select one castle to become his capital, 200,000 storage, 50,000 population and 500% defence bonus. All to be upgraded, I'd be prepared to pay 1000 gold pieces for this option.
1000 gold! Do you know how many ad's I'd have to watch (especially as they don't always pay out). But the idea is a corker. Could you imagine the effort folk would put in to bag one of the big boys. If they are taken they have to be able to be retained by the new owner.