Here's a thought, maybe add a structure to the game.
Examples would be Post #1 comes up with a scneario, Post #2 adds how it would end, then creates a new scenario for #3.
Or, could do a "in seconds". The timing of the post determines what end you get. So if your post is at :33, you get Tuska impacts Gilienor. If you get :44 the Stone of Jas exploded. IF you get :55, Brassica Prime turns the world into a cabbage. If you get :59, Mod Boko unplugged the power cord to the server.