How I think we could have customizable castles and keeps
I know there are good reasons to not make castles and keeps customizable but I do believe there is at least one way to do it. My idea would create a new way for Broadsword to make money, create a gold sink mechanism and reduce the number of castles and keeps that would become customizable so the lag issues aren't a big problem.
Sell a token for 5k or 10k sovereigns in the store that allows a castle or keep to switch to customizable. The owner can use it and convert it to a customizable plot. In the event the castle or keep is traded to another account, it will revert back to the classic style and the token will be placed back into the owners backpack. It will be account bound so you can't trade it to other players. Broadsword will make money and not all castles and keeps will end up being customized.
As far as a gold sink is concerned, create an awesome new polished tile set that only appears if you have purchased the castle customization token. It should only appear in customization menus for castles or keeps. Add a menu in the customization tool that allows you to pay 100 million gold to unlock the tile set and it can be made non-refundable. A one time purchase, no refunds. And since the customizable castle or keep automatically reverts back to its classic style during a trade, you won't have to worry about other players being able to access the function and not have to pay the 100 million.
It may be the dumbest idea about this topic, I don't know.