For that you would need a good map to start with. Picking a map people arent sure of to be succesfull is going to be less interesting or either is going to dissapoint them. And for that we had a contest that went a bit close to that. the 2 skillset contest.or everyone detailing the same map in 72 hours.
Although its too late the next time they could however do a similar contest in 2 seperate moments. In part 1 the map shape gets made, then the voting comes and in part 2 all people are forced to detail only that map. That way you know you are detailing a map that works. And if its a complex map in entity work it adds a chalenge.
Still, for 72h contests i dont recommend full map projects since those take a huge amount of time. a 2k-2k-2k sized area already is quite some size. And those have proven to give much nicer detailed areas.