It is useful to be able to define multiple borders on a world with permission nodes to bypass them individually. Or possibly just a permission node such as worldborder.bypass.5000 to be able to walk 5000 beyond the border. The use-case is for different groups to be able to explore further out on the map, not to replace worldguard or have different overlapping regions.

Also requested here: http://dev.bukkit.org/bukkit-plugins/worldborder/tickets/67-multiple-borders-per-world/

Voting for this issue.

Nice idea..