I love the Idea of a mall. You do /Warp Mall and it brings you to maybe another flat world, basically plots where players can build shops, sign shops or however managment decides to go on this. Or something like SSundees old prison series where a mall is made, and you can create a shop by claiming a section in a real mall and make player based shops besides /market, But the limitation would be what happens when room runs out in the mall, all claims taken? or can a plot world be modified and built(walkways, floor, ceiling etc) to look like your on a mall between different claims. Something where you can modify in configs the spacing between the plots and which block is what.
Example here: