Something that came up when talking with another map maker was me doing a map of theirs, related to a project we will be working on.
So I was thinking that could be cool - pick a map to use as a basis and everyone does their version of that map.
The specifics could be worked out such as just what or how much of the original map must be retained but the style should be up to the competitors.
I think this would produce some interesting results but it would have to be a map that enough people were capable of doing.
So the base map couldn't be so complex as to turn away people from entering.