So I was discussing this idea last night with a coupe of buddies. Basically there is a plugin out for bukkit called ships. I have tested it, it runs very smooth, is updating to 1.7, has nearly no lag, and doesn't mess up oceans when players ride through them. What I suggest, implement this with only having admins the ability to create ships. Make a thread auctioning off 5-10 ships, starting bid would be 30,000 regals. Only for the super rich, so they aren't abused by noobs, and only 5 are made. Once the winner of each auction is decided, (they would have the do 5 seperate auctions) the winner could hire someone to make a ship, or get a designated world staff to build one. The ship would have to be approved by an admin, and then the controls would be added in and it would be moved fr the grid to whatever world the person desires. This would add a lot more role play to the server, and it could be pretty cool for trading routes to be set up for regalia and such. Again this is lag free, configurable so boats can't fly, and doesn't mess up the oceans. When it would come time for a world to be deleted, the ship would be moved. The plugin is seen here. (Ships can be made non editable once they are turned into moving ship) I have seen tons of other servers implement this with no problem, and I believe it would be a great new option for MassiveCraft!
http://dev.bukkit.org/bukkit-plugins/ships/
http://dev.bukkit.org/bukkit-plugins/ships/