The only issue is that people are lazy.
People don't want to make a map and take time out of there lives.
Also, you cannot expand once you place forts on multiple islands. You cannot make more mini-empire islands once people make empires, because the islands you want to make have to be public. A default feature could be a "Public Bricks Mode" in which when you build, all of the bricks are made as a public bricks.