I recall a game I used to play on the PC called Frontier: Elite 2. Included with the box was a small book of short stories. They were essential individual stories in terms of plot, themes and characters, but they were held together by the fact that they were all set in the same place. Or, maybe you're looking at having each writer's characters to have some connection/interaction with each other, (such as with the films Short Cuts and Magnolia).
Okay, so for a location, how about a hotel? Each writer takes a room and populates it with their own characters. As for a connection, aside from the fact they are in the same building, perhaps someone could step up and define some 'global variables' that all stories would be required to recognise, such as a nosey cleaner, an eccentric hotel manager, troublesome guests in another room and so on.
Well, just an idea.