I know this has been talked about before but I really think this would be fun. I would give you the requirements for you tileset and then you would have to create a set overworld area and set dungeon area. So for instance:

Custom Tileset Contest Requirements:

[list=1][*]Tileset must contain grass, dirt and water tiles.[*]Tileset must contain at least one solid bush and one slashable bush.[*]Tileset must contain at least one rock tile.[*]MOST IMPORTANT: Must be 100% original.[/list=1]

This is just an example but this is what it would be like. Of course the sprites and enemies and everything must be made by you. Don't worry about making an actual quest with them but you will be required to create a 10 screen overworld arranged however you like. This must conatin one dungeon showing off your tileset. I think this may give people enough freedom to be creative but still set down some minimum requirements.

So... thoughts? comments?